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Farey sequence

From Rosetta Code
Task
Farey sequence
You are encouraged to solve this task according to the task description, using any language you may know.

The   Farey sequence   Fn   of order   n   is the sequence of completely reduced fractions between   0   and   1   which, when in lowest terms, have denominators less than or equal to   n,   arranged in order of increasing size.

The   Farey sequence   is sometimes incorrectly called a   Farey series.


Each Farey sequence:

  •   starts with the value   0,   denoted by the fraction  
  •   ends with the value   1,   denoted by the fraction   .


The Farey sequences of orders   1   to   5   are:





Task
  •   Compute and show the Farey sequence for orders   1   through   11   (inclusive).
  •   Compute and display the   number   of fractions in the Farey sequence for order   100   through   1,000   (inclusive)   by hundreds.
  •   Show the fractions as   n/d   (using the solidus [or slash] to separate the numerator from the denominator).


See also



AWK[edit]

 
# syntax: GAWK -f FAREY_SEQUENCE.AWK
BEGIN {
for (i=1; i<=11; i++) {
farey(i); printf("\n")
}
for (i=100; i<=1000; i+=100) {
printf(" %d items\n",farey(i))
}
exit(0)
}
function farey(n, a,aa,b,bb,c,cc,d,dd,items,k) {
a = 0; b = 1; c = 1; d = n
printf("%d:",n)
if (n <= 11) {
printf(" %d/%d",a,b)
}
while (c <= n) {
k = int((n+b)/d)
aa = c; bb = d; cc = k*c-a; dd = k*d-b
a = aa; b = bb; c = cc; d = dd
items++
if (n <= 11) {
printf(" %d/%d",a,b)
}
}
return(1+items)
}
 
Output:
1: 0/1 1/1
2: 0/1 1/2 1/1
3: 0/1 1/3 1/2 2/3 1/1
4: 0/1 1/4 1/3 1/2 2/3 3/4 1/1
5: 0/1 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 1/1
6: 0/1 1/6 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 5/6 1/1
7: 0/1 1/7 1/6 1/5 1/4 2/7 1/3 2/5 3/7 1/2 4/7 3/5 2/3 5/7 3/4 4/5 5/6 6/7 1/1
8: 0/1 1/8 1/7 1/6 1/5 1/4 2/7 1/3 3/8 2/5 3/7 1/2 4/7 3/5 5/8 2/3 5/7 3/4 4/5 5/6 6/7 7/8 1/1
9: 0/1 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 1/1
10: 0/1 1/10 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 3/10 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 7/10 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 9/10 1/1
11: 0/1 1/11 1/10 1/9 1/8 1/7 1/6 2/11 1/5 2/9 1/4 3/11 2/7 3/10 1/3 4/11 3/8 2/5 3/7 4/9 5/11 1/2 6/11 5/9 4/7 3/5 5/8 7/11 2/3 7/10 5/7 8/11 3/4 7/9 4/5 9/11 5/6 6/7 7/8 8/9 9/10 10/11 1/1
100: 3045 items
200: 12233 items
300: 27399 items
400: 48679 items
500: 76117 items
600: 109501 items
700: 149019 items
800: 194751 items
900: 246327 items
1000: 304193 items

C[edit]

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
void farey(int n)
{
typedef struct { int d, n; } frac;
frac f1 = {0, 1}, f2 = {1, n}, t;
int k;
 
printf("%d/%d %d/%d", 0, 1, 1, n);
while (f2.n > 1) {
k = (n + f1.n) / f2.n;
t = f1, f1 = f2, f2 = (frac) { f2.d * k - t.d, f2.n * k - t.n };
printf(" %d/%d", f2.d, f2.n);
}
 
putchar('\n');
}
 
typedef unsigned long long ull;
ull *cache;
size_t ccap;
 
ull farey_len(int n)
{
if (n >= ccap) {
size_t old = ccap;
if (!ccap) ccap = 16;
while (ccap <= n) ccap *= 2;
cache = realloc(cache, sizeof(ull) * ccap);
memset(cache + old, 0, sizeof(ull) * (ccap - old));
} else if (cache[n])
return cache[n];
 
ull len = (ull)n*(n + 3) / 2;
int p, q = 0;
for (p = 2; p <= n; p = q) {
q = n/(n/p) + 1;
len -= farey_len(n/p) * (q - p);
}
 
cache[n] = len;
return len;
}
 
int main(void)
{
int n;
for (n = 1; n <= 11; n++) {
printf("%d: ", n);
farey(n);
}
 
for (n = 100; n <= 1000; n += 100)
printf("%d: %llu items\n", n, farey_len(n));
 
n = 10000000;
printf("\n%d: %llu items\n", n, farey_len(n));
return 0;
}
Output:
1: 0/1 1/1
2: 0/1 1/2 1/1
3: 0/1 1/3 1/2 2/3 1/1
4: 0/1 1/4 1/3 1/2 2/3 3/4 1/1
5: 0/1 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 1/1
6: 0/1 1/6 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 5/6 1/1
7: 0/1 1/7 1/6 1/5 1/4 2/7 1/3 2/5 3/7 1/2 4/7 3/5 2/3 5/7 3/4 4/5 5/6 6/7 1/1
8: 0/1 1/8 1/7 1/6 1/5 1/4 2/7 1/3 3/8 2/5 3/7 1/2 4/7 3/5 5/8 2/3 5/7 3/4 4/5 5/6 6/7 7/8 1/1
9: 0/1 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 1/1
10: 0/1 1/10 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 3/10 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 7/10 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 9/10 1/1
11: 0/1 1/11 1/10 1/9 1/8 1/7 1/6 2/11 1/5 2/9 1/4 3/11 2/7 3/10 1/3 4/11 3/8 2/5 3/7 4/9 5/11 1/2 6/11 5/9 4/7 3/5 5/8 7/11 2/3 7/10 5/7 8/11 3/4 7/9 4/5 9/11 5/6 6/7 7/8 8/9 9/10 10/11 1/1
100: 3045 items
200: 12233 items
300: 27399 items
400: 48679 items
500: 76117 items
600: 109501 items
700: 149019 items
800: 194751 items
900: 246327 items
1000: 304193 items

10000000: 30396356427243 items

D[edit]

This imports the module from the Arithmetic/Rational task.

import std.stdio, std.algorithm, std.range, arithmetic_rational;
 
auto farey(in int n) pure nothrow @safe {
return rational(0, 1).only.chain(
iota(1, n + 1)
.map!(k => iota(1, k + 1).map!(m => rational(m, k)))
.join.sort().uniq);
}
 
void main() @safe {
writefln("Farey sequence for order 1 through 11:\n%(%s\n%)",
iota(1, 12).map!farey);
writeln("\nFarey sequence fractions, 100 to 1000 by hundreds:\n",
iota(100, 1_001, 100).map!(i => i.farey.walkLength));
}
Output:
Farey sequence for order 1 through 11:
[0, 1]
[0, 1/2, 1]
[0, 1/3, 1/2, 2/3, 1]
[0, 1/4, 1/3, 1/2, 2/3, 3/4, 1]
[0, 1/5, 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 1]
[0, 1/6, 1/5, 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 1]
[0, 1/7, 1/6, 1/5, 1/4, 2/7, 1/3, 2/5, 3/7, 1/2, 4/7, 3/5, 2/3, 5/7, 3/4, 4/5, 5/6, 6/7, 1]
[0, 1/8, 1/7, 1/6, 1/5, 1/4, 2/7, 1/3, 3/8, 2/5, 3/7, 1/2, 4/7, 3/5, 5/8, 2/3, 5/7, 3/4, 4/5, 5/6, 6/7, 7/8, 1]
[0, 1/9, 1/8, 1/7, 1/6, 1/5, 2/9, 1/4, 2/7, 1/3, 3/8, 2/5, 3/7, 4/9, 1/2, 5/9, 4/7, 3/5, 5/8, 2/3, 5/7, 3/4, 7/9, 4/5, 5/6, 6/7, 7/8, 8/9, 1]
[0, 1/10, 1/9, 1/8, 1/7, 1/6, 1/5, 2/9, 1/4, 2/7, 3/10, 1/3, 3/8, 2/5, 3/7, 4/9, 1/2, 5/9, 4/7, 3/5, 5/8, 2/3, 7/10, 5/7, 3/4, 7/9, 4/5, 5/6, 6/7, 7/8, 8/9, 9/10, 1]
[0, 1/11, 1/10, 1/9, 1/8, 1/7, 1/6, 2/11, 1/5, 2/9, 1/4, 3/11, 2/7, 3/10, 1/3, 4/11, 3/8, 2/5, 3/7, 4/9, 5/11, 1/2, 6/11, 5/9, 4/7, 3/5, 5/8, 7/11, 2/3, 7/10, 5/7, 8/11, 3/4, 7/9, 4/5, 9/11, 5/6, 6/7, 7/8, 8/9, 9/10, 10/11, 1]

Farey sequence fractions, 100 to 1000 by hundreds:
[3045, 12233, 27399, 48679, 76117, 109501, 149019, 194751, 246327, 304193]

Alternative Version[edit]

This is as fast as the C entry (total run-time is 0.20 seconds).

Translation of: C
import core.stdc.stdio: printf, putchar;
 
void farey(in uint n) nothrow @nogc {
static struct Frac { uint d, n; }
 
Frac f1 = { 0, 1 }, f2 = { 1, n };
 
printf("%u/%u %u/%u", 0, 1, 1, n);
while (f2.n > 1) {
immutable k = (n + f1.n) / f2.n;
immutable aux = f1;
f1 = f2;
f2 = Frac(f2.d * k - aux.d, f2.n * k - aux.n);
printf(" %u/%u", f2.d, f2.n);
}
 
putchar('\n');
}
 
ulong fareyLength(in uint n, ref ulong[] cache) pure nothrow @safe {
if (n >= cache.length) {
auto newLen = cache.length;
if (newLen == 0)
newLen = 16;
while (newLen <= n)
newLen *= 2;
cache.length = newLen;
} else if (cache[n])
return cache[n];
 
ulong len = ulong(n) * (n + 3) / 2;
for (uint p = 2, q = 0; p <= n; p = q) {
q = n / (n / p) + 1;
len -= fareyLength(n / p, cache) * (q - p);
}
 
cache[n] = len;
return len;
}
 
void main() nothrow {
foreach (immutable uint n; 1 .. 12) {
printf("%u: ", n);
n.farey;
}
 
ulong[] cache;
for (uint n = 100; n <= 1_000; n += 100)
printf("%u: %llu items\n", n, fareyLength(n, cache));
 
immutable uint n = 10_000_000;
printf("\n%u: %llu items\n", n, fareyLength(n, cache));
}
Output:
1: 0/1 1/1
2: 0/1 1/2 1/1
3: 0/1 1/3 1/2 2/3 1/1
4: 0/1 1/4 1/3 1/2 2/3 3/4 1/1
5: 0/1 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 1/1
6: 0/1 1/6 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 5/6 1/1
7: 0/1 1/7 1/6 1/5 1/4 2/7 1/3 2/5 3/7 1/2 4/7 3/5 2/3 5/7 3/4 4/5 5/6 6/7 1/1
8: 0/1 1/8 1/7 1/6 1/5 1/4 2/7 1/3 3/8 2/5 3/7 1/2 4/7 3/5 5/8 2/3 5/7 3/4 4/5 5/6 6/7 7/8 1/1
9: 0/1 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 1/1
10: 0/1 1/10 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 3/10 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 7/10 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 9/10 1/1
11: 0/1 1/11 1/10 1/9 1/8 1/7 1/6 2/11 1/5 2/9 1/4 3/11 2/7 3/10 1/3 4/11 3/8 2/5 3/7 4/9 5/11 1/2 6/11 5/9 4/7 3/5 5/8 7/11 2/3 7/10 5/7 8/11 3/4 7/9 4/5 9/11 5/6 6/7 7/8 8/9 9/10 10/11 1/1
100: 3045 items
200: 12233 items
300: 27399 items
400: 48679 items
500: 76117 items
600: 109501 items
700: 149019 items
800: 194751 items
900: 246327 items
1000: 304193 items

10000000: 30396356427243 items

EchoLisp[edit]

 
(define distinct-divisors
(compose make-set prime-factors))
 
;; euler totient : Φ : n / product(p_i) * product (p_i - 1)
;; # of divisors <= n
 
(define (Φ n)
(let ((pdiv (distinct-divisors n)))
(/ (* n (for/product ((p pdiv)) (1- p))) (for/product ((p pdiv)) p))))
 
;; farey-sequence length |Fn| = 1 + sigma (m=1..) Φ(m)
 
(define ( F-length n) (1+ (for/sum ((m (1+ n))) (Φ m))))
 
;; farey sequence
;; apply the definition : O(n^2)
(define (Farey N)
(set! N (1+ N))
(make-set (for*/list ((n N) (d (in-range n N))) (rational n d))))
 
 
Output:
 
(for ((n (in-range 1 12))) ( printf "F(%d) %s" n (Farey n)))
F(1) { 0 1 }
F(2) { 0 1/2 1 }
F(3) { 0 1/3 1/2 2/3 1 }
F(4) { 0 1/4 1/3 1/2 2/3 3/4 1 }
F(5) { 0 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 1 }
F(6) { 0 1/6 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 5/6 1 }
F(7) { 0 1/7 1/6 1/5 1/4 2/7 1/3 2/5 3/7 1/2 4/7 3/5 2/3 5/7 3/4 4/5 5/6 6/7 1 }
F(8) { 0 1/8 1/7 1/6 1/5 1/4 2/7 1/3 3/8 2/5 3/7 1/2 4/7 3/5 5/8 2/3 5/7 3/4 4/5 5/6 6/7 7/8 1 }
F(9) { 0 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 1 }
F(10) { 0 1/10 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 3/10 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 7/10 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 9/10 1 }
F(11) { 0 1/11 1/10 1/9 1/8 1/7 1/6 2/11 1/5 2/9 1/4 3/11 2/7 3/10 1/3 4/11 3/8 2/5 3/7 4/9 5/11 1/2 6/11 5/9 4/7 3/5 5/8 7/11 2/3 7/10 5/7 8/11 3/4 7/9 4/5 9/11 5/6 6/7 7/8 8/9 9/10 10/11 1 }
 
(for (( n (in-range 100 1100 100))) (printf "|F(%d)| = %d" n (F-length n)))
|F(100)| = 3045
|F(200)| = 12233
|F(300)| = 27399
|F(400)| = 48679
|F(500)| = 76117
|F(600)| = 109501
|F(700)| = 149019
|F(800)| = 194751
|F(900)| = 246327
|F(1000)| = 304193
 
(for (( n '(10_000 100_000))) (printf "|F(%d)| = %d" n (F-length n)))
|F(10000)| = 30397487
|F(100000)| = 3039650755
 

FunL[edit]

Translation of Python code at [1].

def farey( n ) =
res = seq()
a, b, c, d = 0, 1, 1, n
res += "$a/$b"
 
while c <= n
k = (n + b)\d
a, b, c, d = c, d, k*c - a, k*d - b
res += "$a/$b"
 
for i <- 1..11
println( "$i: ${farey(i).mkString(', ')}" )
 
for i <- 100..1000 by 100
println( "$i: ${farey(i).length()}" )
Output:
1: 0/1, 1/1
2: 0/1, 1/2, 1/1
3: 0/1, 1/3, 1/2, 2/3, 1/1
4: 0/1, 1/4, 1/3, 1/2, 2/3, 3/4, 1/1
5: 0/1, 1/5, 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 1/1
6: 0/1, 1/6, 1/5, 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 1/1
7: 0/1, 1/7, 1/6, 1/5, 1/4, 2/7, 1/3, 2/5, 3/7, 1/2, 4/7, 3/5, 2/3, 5/7, 3/4, 4/5, 5/6, 6/7, 1/1
8: 0/1, 1/8, 1/7, 1/6, 1/5, 1/4, 2/7, 1/3, 3/8, 2/5, 3/7, 1/2, 4/7, 3/5, 5/8, 2/3, 5/7, 3/4, 4/5, 5/6, 6/7, 7/8, 1/1
9: 0/1, 1/9, 1/8, 1/7, 1/6, 1/5, 2/9, 1/4, 2/7, 1/3, 3/8, 2/5, 3/7, 4/9, 1/2, 5/9, 4/7, 3/5, 5/8, 2/3, 5/7, 3/4, 7/9, 4/5, 5/6, 6/7, 7/8, 8/9, 1/1
10: 0/1, 1/10, 1/9, 1/8, 1/7, 1/6, 1/5, 2/9, 1/4, 2/7, 3/10, 1/3, 3/8, 2/5, 3/7, 4/9, 1/2, 5/9, 4/7, 3/5, 5/8, 2/3, 7/10, 5/7, 3/4, 7/9, 4/5, 5/6, 6/7, 7/8, 8/9, 9/10, 1/1
11: 0/1, 1/11, 1/10, 1/9, 1/8, 1/7, 1/6, 2/11, 1/5, 2/9, 1/4, 3/11, 2/7, 3/10, 1/3, 4/11, 3/8, 2/5, 3/7, 4/9, 5/11, 1/2, 6/11, 5/9, 4/7, 3/5, 5/8, 7/11, 2/3, 7/10, 5/7, 8/11, 3/4, 7/9, 4/5, 9/11, 5/6, 6/7, 7/8, 8/9, 9/10, 10/11, 1/1
100: 3045
200: 12233
300: 27399
400: 48679
500: 76117
600: 109501
700: 149019
800: 194751
900: 246327
1000: 304193

Go[edit]

package main
 
import "fmt"
 
type frac struct{ num, den int }
 
func (f frac) String() string {
return fmt.Sprintf("%d/%d", f.num, f.den)
}
 
func f(l, r frac, n int) {
m := frac{l.num + r.num, l.den + r.den}
if m.den <= n {
f(l, m, n)
fmt.Print(m, " ")
f(m, r, n)
}
}
 
func main() {
// task 1. solution by recursive generation of mediants
for n := 1; n <= 11; n++ {
l := frac{0, 1}
r := frac{1, 1}
fmt.Printf("F(%d): %s ", n, l)
f(l, r, n)
fmt.Println(r)
}
// task 2. direct solution by summing totient function
// 2.1 generate primes to 1000
var composite [1001]bool
for _, p := range []int{2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31} {
for n := p * 2; n <= 1000; n += p {
composite[n] = true
}
}
// 2.2 generate totients to 1000
var tot [1001]int
for i := range tot {
tot[i] = 1
}
for n := 2; n <= 1000; n++ {
if !composite[n] {
tot[n] = n - 1
for a := n * 2; a <= 1000; a += n {
f := n - 1
for r := a / n; r%n == 0; r /= n {
f *= n
}
tot[a] *= f
}
}
}
// 2.3 sum totients
for n, sum := 1, 1; n <= 1000; n++ {
sum += tot[n]
if n%100 == 0 {
fmt.Printf("|F(%d)|: %d\n", n, sum)
}
}
}
Output:
F(1): 0/1 1/1
F(2): 0/1 1/2 1/1
F(3): 0/1 1/3 1/2 2/3 1/1
F(4): 0/1 1/4 1/3 1/2 2/3 3/4 1/1
F(5): 0/1 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 1/1
F(6): 0/1 1/6 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 5/6 1/1
F(7): 0/1 1/7 1/6 1/5 1/4 2/7 1/3 2/5 3/7 1/2 4/7 3/5 2/3 5/7 3/4 4/5 5/6 6/7 1/1
F(8): 0/1 1/8 1/7 1/6 1/5 1/4 2/7 1/3 3/8 2/5 3/7 1/2 4/7 3/5 5/8 2/3 5/7 3/4 4/5 5/6 6/7 7/8 1/1
F(9): 0/1 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 1/1
F(10): 0/1 1/10 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 3/10 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 7/10 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 9/10 1/1
F(11): 0/1 1/11 1/10 1/9 1/8 1/7 1/6 2/11 1/5 2/9 1/4 3/11 2/7 3/10 1/3 4/11 3/8 2/5 3/7 4/9 5/11 1/2 6/11 5/9 4/7 3/5 5/8 7/11 2/3 7/10 5/7 8/11 3/4 7/9 4/5 9/11 5/6 6/7 7/8 8/9 9/10 10/11 1/1
|F(100)|: 3045
|F(200)|: 12233
|F(300)|: 27399
|F(400)|: 48679
|F(500)|: 76117
|F(600)|: 109501
|F(700)|: 149019
|F(800)|: 194751
|F(900)|: 246327
|F(1000)|: 304193


Haskell[edit]

Generating an n'th order Farey sequence follows the algorithm described in Wikipedia. However, for fun, to generate a list of Farey sequences we generate only the highest order sequence, creating the rest by successively pruning the original.

import Data.List (unfoldr, mapAccumR)
import Data.Ratio ((%), denominator, numerator)
import Text.Printf (PrintfArg, printf)
 
-- The n'th order Farey sequence.
farey :: Integer -> [Rational]
farey n = 0 : unfoldr step (0, 1, 1, n)
where
step (a, b, c, d)
| c > n = Nothing
| otherwise =
let k = (n + b) `quot` d
in Just (c %d, (c, d, k * c - a, k * d - b))
 
-- A list of pairs, (n, fn n), where fn is a function applied to the n'th order
-- Farey sequence. We assume the list of orders is increasing. Only the
-- highest order Farey sequence is evaluated; the remainder are generated by
-- successively pruning this sequence.
fareys :: ([Rational] -> a) -> [Integer] -> [(Integer, a)]
fareys fn ns = snd $ mapAccumR prune (farey $ last ns) ns
where
prune rs n =
let rs'' = filter ((<= n) . denominator) rs
in (rs'', (n, fn rs''))
 
fprint
:: (PrintfArg b)
=> String -> [(Integer, b)] -> IO ()
fprint fmt = mapM_ (uncurry $ printf fmt)
 
showFracs :: [Rational] -> String
showFracs =
unwords .
map
(concat . ([show . numerator, const "/", show . denominator] <*>) . pure)
 
main :: IO ()
main = do
putStrLn "Farey Sequences\n"
fprint "%2d %s\n" $ fareys showFracs [1 .. 11]
putStrLn "\nSequence Lengths\n"
fprint "%4d %d\n" $ fareys length [100,200 .. 1000]

Output:

Farey Sequences

 1 0/1 1/1
 2 0/1 1/2 1/1
 3 0/1 1/3 1/2 2/3 1/1
 4 0/1 1/4 1/3 1/2 2/3 3/4 1/1
 5 0/1 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 1/1
 6 0/1 1/6 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 5/6 1/1
 7 0/1 1/7 1/6 1/5 1/4 2/7 1/3 2/5 3/7 1/2 4/7 3/5 2/3 5/7 3/4 4/5 5/6 6/7 1/1
 8 0/1 1/8 1/7 1/6 1/5 1/4 2/7 1/3 3/8 2/5 3/7 1/2 4/7 3/5 5/8 2/3 5/7 3/4 4/5 5/6 6/7 7/8 1/1
 9 0/1 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 1/1
10 0/1 1/10 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 3/10 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 7/10 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 9/10 1/1
11 0/1 1/11 1/10 1/9 1/8 1/7 1/6 2/11 1/5 2/9 1/4 3/11 2/7 3/10 1/3 4/11 3/8 2/5 3/7 4/9 5/11 1/2 6/11 5/9 4/7 3/5 5/8 7/11 2/3 7/10 5/7 8/11 3/4 7/9 4/5 9/11 5/6 6/7 7/8 8/9 9/10 10/11 1/1

Sequence Lengths

 100 3045
 200 12233
 300 27399
 400 48679
 500 76117
 600 109501
 700 149019
 800 194751
 900 246327
1000 304193

J[edit]

J has an internal data representation for completely reduced rational numbers. This displays as integers where that is possible and otherwise displays as NNNrDDD where the part to the left of the 'r' is the numerator and the part to the right of the 'r' is the denominator.

This mechanism is a part of J's "constant language", and is similar to scientific notation (which uses an 'e' instead of an 'r') and with J's complex number notation (which uses a 'j' instead of an 'r'), and which follow similar display rules.

This mechanism also hints that J's type promotion rules are designed to give internally consistent results a priority. As much as possible you do not get different results from the same operation just because you "used a different data type". J's design adopts the philosophy that "different results from the same operation based on different types" is likely to introduce errors in thinking. (Of course there are machine limits and certain floating point operations tend to introduce internal inconsistencies, but those are mentioned only in passing - they are not directly relevant to this task.)

Farey=:3 :0
0,/:~~.(#~ <:&1),%/~1x+i.y
)

Required examples:

   Farey 1
0 1
Farey 2
0 1r2 1
Farey 3
0 1r3 1r2 2r3 1
Farey 4
0 1r4 1r3 1r2 2r3 3r4 1
Farey 5
0 1r5 1r4 1r3 2r5 1r2 3r5 2r3 3r4 4r5 1
Farey 6
0 1r6 1r5 1r4 1r3 2r5 1r2 3r5 2r3 3r4 4r5 5r6 1
Farey 7
0 1r7 1r6 1r5 1r4 2r7 1r3 2r5 3r7 1r2 4r7 3r5 2r3 5r7 3r4 4r5 5r6 6r7 1
Farey 8
0 1r8 1r7 1r6 1r5 1r4 2r7 1r3 3r8 2r5 3r7 1r2 4r7 3r5 5r8 2r3 5r7 3r4 4r5 5r6 6r7 7r8 1
Farey 9
0 1r9 1r8 1r7 1r6 1r5 2r9 1r4 2r7 1r3 3r8 2r5 3r7 4r9 1r2 5r9 4r7 3r5 5r8 2r3 5r7 3r4 7r9 4r5 5r6 6r7 7r8 8r9 1
Farey 10
0 1r10 1r9 1r8 1r7 1r6 1r5 2r9 1r4 2r7 3r10 1r3 3r8 2r5 3r7 4r9 1r2 5r9 4r7 3r5 5r8 2r3 7r10 5r7 3r4 7r9 4r5 5r6 6r7 7r8 8r9 9r10 1
Farey 11
0 1r11 1r10 1r9 1r8 1r7 1r6 2r11 1r5 2r9 1r4 3r11 2r7 3r10 1r3 4r11 3r8 2r5 3r7 4r9 5r11 1r2 6r11 5r9 4r7 3r5 5r8 7r11 2r3 7r10 5r7 8r11 3r4 7r9 4r5 9r11 5r6 6r7 7r8 8r9 9r10 10r11 1
(,. [email protected]"0) 100*1+i.10
100 3045
200 12233
300 27399
400 48679
500 76117
600 109501
700 149019
800 194751
900 246327
1000 304193

Optimized[edit]

A small change in the 'Farey' function makes the last request, faster.

A second change in the 'Farey' function makes the last request, much faster.

A third change in the 'Farey' function makes the last request, again, a little bit faster.

Even if it is 20 times faster, the response time is just acceptable. Now the response time is quite satisfactory.

The script produces the sequences in rational number notation as well in fractional number notation.

Farey=: 3 : '/:~,&0 1~.(#~<&1),(1&+%/2&+)i.y-1'
 
NB. rational number notation
rplc&(' 0';'= 0r0');,&('r1',LF)@:,~&'F'@:":@:x:&.>(,Farey)&.>1+i.11
 
NB. fractional number notation
rplc&('r';'/';' 0';'= 0/0');,&('r1',LF)@:,~&'F'@:":@:x:&.>(,Farey)&.>1+i.11
 
NB. number of fractions
;,&(' items',LF)@:,~&'F'@:":&.>(,.#@:Farey)&.>100*1+i.10
Output:
F1= 0r0 1r1
F2= 0r0 1r2 1r1
F3= 0r0 1r3 1r2 2r3 1r1
F4= 0r0 1r4 1r3 1r2 2r3 3r4 1r1
F5= 0r0 1r5 1r4 1r3 2r5 1r2 3r5 2r3 3r4 4r5 1r1
F6= 0r0 1r6 1r5 1r4 1r3 2r5 1r2 3r5 2r3 3r4 4r5 5r6 1r1
F7= 0r0 1r7 1r6 1r5 1r4 2r7 1r3 2r5 3r7 1r2 4r7 3r5 2r3 5r7 3r4 4r5 5r6 6r7 1r1
F8= 0r0 1r8 1r7 1r6 1r5 1r4 2r7 1r3 3r8 2r5 3r7 1r2 4r7 3r5 5r8 2r3 5r7 3r4 4r5 5r6 6r7 7r8 1r1
F9= 0r0 1r9 1r8 1r7 1r6 1r5 2r9 1r4 2r7 1r3 3r8 2r5 3r7 4r9 1r2 5r9 4r7 3r5 5r8 2r3 5r7 3r4 7r9 4r5 5r6 6r7 7r8 8r9 1r1
F10= 0r0 1r10 1r9 1r8 1r7 1r6 1r5 2r9 1r4 2r7 3r10 1r3 3r8 2r5 3r7 4r9 1r2 5r9 4r7 3r5 5r8 2r3 7r10 5r7 3r4 7r9 4r5 5r6 6r7 7r8 8r9 9r10 1r1
F11= 0r0 1r11 1r10 1r9 1r8 1r7 1r6 2r11 1r5 2r9 1r4 3r11 2r7 3r10 1r3 4r11 3r8 2r5 3r7 4r9 5r11 1r2 6r11 5r9 4r7 3r5 5r8 7r11 2r3 7r10 5r7 8r11 3r4 7r9 4r5 9r11 5r6 6r7 7r8 8r9 9r10 10r11 1r1

F1= 0/0 1/1
F2= 0/0 1/2 1/1
F3= 0/0 1/3 1/2 2/3 1/1
F4= 0/0 1/4 1/3 1/2 2/3 3/4 1/1
F5= 0/0 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 1/1
F6= 0/0 1/6 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 5/6 1/1
F7= 0/0 1/7 1/6 1/5 1/4 2/7 1/3 2/5 3/7 1/2 4/7 3/5 2/3 5/7 3/4 4/5 5/6 6/7 1/1
F8= 0/0 1/8 1/7 1/6 1/5 1/4 2/7 1/3 3/8 2/5 3/7 1/2 4/7 3/5 5/8 2/3 5/7 3/4 4/5 5/6 6/7 7/8 1/1
F9= 0/0 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 1/1
F10= 0/0 1/10 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 3/10 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 7/10 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 9/10 1/1
F11= 0/0 1/11 1/10 1/9 1/8 1/7 1/6 2/11 1/5 2/9 1/4 3/11 2/7 3/10 1/3 4/11 3/8 2/5 3/7 4/9 5/11 1/2 6/11 5/9 4/7 3/5 5/8 7/11 2/3 7/10 5/7 8/11 3/4 7/9 4/5 9/11 5/6 6/7 7/8 8/9 9/10 10/11 1/1

F100 3045 items
F200 12233 items
F300 27399 items
F400 48679 items
F500 76117 items
F600 109501 items
F700 149019 items
F800 194751 items
F900 246327 items
F1000 304193 items

Java[edit]

Works with: Java version 1.5+

This example uses the fact that it generates the fraction candidates from the bottom up as well as Set's internal duplicate removal (based on Comparable.compareTo) to get rid of un-reduced fractions. It also uses TreeSet to sort based on the value of the fraction.

import java.util.TreeSet;
 
public class Farey{
private static class Frac implements Comparable<Frac>{
int num;
int den;
 
public Frac(int num, int den){
this.num = num;
this.den = den;
}
 
@Override
public String toString(){
return num + " / " + den;
}
 
@Override
public int compareTo(Frac o){
return Double.compare((double)num / den, (double)o.num / o.den);
}
}
 
public static TreeSet<Frac> genFarey(int i){
TreeSet<Frac> farey = new TreeSet<Frac>();
for(int den = 1; den <= i; den++){
for(int num = 0; num <= den; num++){
farey.add(new Frac(num, den));
}
}
return farey;
}
 
public static void main(String[] args){
for(int i = 1; i <= 11; i++){
System.out.println("F" + i + ": " + genFarey(i));
}
 
for(int i = 100; i <= 1000; i += 100){
System.out.println("F" + i + ": " + genFarey(i).size() + " members");
}
}
}
Output:
F1: [0 / 1, 1 / 1]
F2: [0 / 1, 1 / 2, 1 / 1]
F3: [0 / 1, 1 / 3, 1 / 2, 2 / 3, 1 / 1]
F4: [0 / 1, 1 / 4, 1 / 3, 1 / 2, 2 / 3, 3 / 4, 1 / 1]
F5: [0 / 1, 1 / 5, 1 / 4, 1 / 3, 2 / 5, 1 / 2, 3 / 5, 2 / 3, 3 / 4, 4 / 5, 1 / 1]
F6: [0 / 1, 1 / 6, 1 / 5, 1 / 4, 1 / 3, 2 / 5, 1 / 2, 3 / 5, 2 / 3, 3 / 4, 4 / 5, 5 / 6, 1 / 1]
F7: [0 / 1, 1 / 7, 1 / 6, 1 / 5, 1 / 4, 2 / 7, 1 / 3, 2 / 5, 3 / 7, 1 / 2, 4 / 7, 3 / 5, 2 / 3, 5 / 7, 3 / 4, 4 / 5, 5 / 6, 6 / 7, 1 / 1]
F8: [0 / 1, 1 / 8, 1 / 7, 1 / 6, 1 / 5, 1 / 4, 2 / 7, 1 / 3, 3 / 8, 2 / 5, 3 / 7, 1 / 2, 4 / 7, 3 / 5, 5 / 8, 2 / 3, 5 / 7, 3 / 4, 4 / 5, 5 / 6, 6 / 7, 7 / 8, 1 / 1]
F9: [0 / 1, 1 / 9, 1 / 8, 1 / 7, 1 / 6, 1 / 5, 2 / 9, 1 / 4, 2 / 7, 1 / 3, 3 / 8, 2 / 5, 3 / 7, 4 / 9, 1 / 2, 5 / 9, 4 / 7, 3 / 5, 5 / 8, 2 / 3, 5 / 7, 3 / 4, 7 / 9, 4 / 5, 5 / 6, 6 / 7, 7 / 8, 8 / 9, 1 / 1]
F10: [0 / 1, 1 / 10, 1 / 9, 1 / 8, 1 / 7, 1 / 6, 1 / 5, 2 / 9, 1 / 4, 2 / 7, 3 / 10, 1 / 3, 3 / 8, 2 / 5, 3 / 7, 4 / 9, 1 / 2, 5 / 9, 4 / 7, 3 / 5, 5 / 8, 2 / 3, 7 / 10, 5 / 7, 3 / 4, 7 / 9, 4 / 5, 5 / 6, 6 / 7, 7 / 8, 8 / 9, 9 / 10, 1 / 1]
F11: [0 / 1, 1 / 11, 1 / 10, 1 / 9, 1 / 8, 1 / 7, 1 / 6, 2 / 11, 1 / 5, 2 / 9, 1 / 4, 3 / 11, 2 / 7, 3 / 10, 1 / 3, 4 / 11, 3 / 8, 2 / 5, 3 / 7, 4 / 9, 5 / 11, 1 / 2, 6 / 11, 5 / 9, 4 / 7, 3 / 5, 5 / 8, 7 / 11, 2 / 3, 7 / 10, 5 / 7, 8 / 11, 3 / 4, 7 / 9, 4 / 5, 9 / 11, 5 / 6, 6 / 7, 7 / 8, 8 / 9, 9 / 10, 10 / 11, 1 / 1]
F100: 3045 members
F200: 12233 members
F300: 27399 members
F400: 48679 members
F500: 76117 members
F600: 109501 members
F700: 149019 members
F800: 194751 members
F900: 246327 members
F1000: 304193 members

Kotlin[edit]

// version 1.1
 
fun farey(n: Int): List<String> {
var a = 0
var b = 1
var c = 1
var d = n
val f = mutableListOf("$a/$b")
while (c <= n) {
val k = (n + b) / d
val aa = a
val bb = b
a = c
b = d
c = k * c - aa
d = k * d - bb
f.add("$a/$b")
}
return f.toList()
}
 
fun main(args: Array<String>) {
for (i in 1..11)
println("${"%2d".format(i)}: ${farey(i).joinToString(" ")}")
println()
for (i in 100..1000 step 100)
println("${"%4d".format(i)}: ${"%6d".format(farey(i).size)} fractions")
}
Output:
 1: 0/1 1/1
 2: 0/1 1/2 1/1
 3: 0/1 1/3 1/2 2/3 1/1
 4: 0/1 1/4 1/3 1/2 2/3 3/4 1/1
 5: 0/1 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 1/1
 6: 0/1 1/6 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 5/6 1/1
 7: 0/1 1/7 1/6 1/5 1/4 2/7 1/3 2/5 3/7 1/2 4/7 3/5 2/3 5/7 3/4 4/5 5/6 6/7 1/1
 8: 0/1 1/8 1/7 1/6 1/5 1/4 2/7 1/3 3/8 2/5 3/7 1/2 4/7 3/5 5/8 2/3 5/7 3/4 4/5 5/6 6/7 7/8 1/1
 9: 0/1 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 1/1
10: 0/1 1/10 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 3/10 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 7/10 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 9/10 1/1
11: 0/1 1/11 1/10 1/9 1/8 1/7 1/6 2/11 1/5 2/9 1/4 3/11 2/7 3/10 1/3 4/11 3/8 2/5 3/7 4/9 5/11 1/2 6/11 5/9 4/7 3/5 5/8 7/11 2/3 7/10 5/7 8/11 3/4 7/9 4/5 9/11 5/6 6/7 7/8 8/9 9/10 10/11 1/1

 100:   3045 fractions
 200:  12233 fractions
 300:  27399 fractions
 400:  48679 fractions
 500:  76117 fractions
 600: 109501 fractions
 700: 149019 fractions
 800: 194751 fractions
 900: 246327 fractions
1000: 304193 fractions

Lua[edit]

-- Return farey sequence of order n
function farey (n)
local a, b, c, d, k = 0, 1, 1, n
local farTab = {{a, b}}
while c <= n do
k = math.floor((n + b) / d)
a, b, c, d = c, d, k * c - a, k * d - b
table.insert(farTab, {a, b})
end
return farTab
end
 
-- Main procedure
for i = 1, 11 do
io.write(i .. ": ")
for _, frac in pairs(farey(i)) do io.write(frac[1] .. "/" .. frac[2] .. " ") end
print()
end
for i = 100, 1000, 100 do print(i .. ": " .. #farey(i) .. " items") end
Output:
1: 0/1 1/1
2: 0/1 1/2 1/1
3: 0/1 1/3 1/2 2/3 1/1
4: 0/1 1/4 1/3 1/2 2/3 3/4 1/1
5: 0/1 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 1/1
6: 0/1 1/6 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 5/6 1/1
7: 0/1 1/7 1/6 1/5 1/4 2/7 1/3 2/5 3/7 1/2 4/7 3/5 2/3 5/7 3/4 4/5 5/6 6/7 1/1
8: 0/1 1/8 1/7 1/6 1/5 1/4 2/7 1/3 3/8 2/5 3/7 1/2 4/7 3/5 5/8 2/3 5/7 3/4 4/5 5/6 6/7 7/8 1/1
9: 0/1 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 1/1
10: 0/1 1/10 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 3/10 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 7/10 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 9/10 1/1
11: 0/1 1/11 1/10 1/9 1/8 1/7 1/6 2/11 1/5 2/9 1/4 3/11 2/7 3/10 1/3 4/11 3/8 2/5 3/7 4/9 5/11 1/2 6/11 5/9 4/7 3/5 5/8 7/11 2/3 7/10 5/7 8/11 3/4 7/9 4/5 9/11 5/6 6/7 7/8 8/9 9/10 10/11 1/1
100: 3045 items
200: 12233 items
300: 27399 items
400: 48679 items
500: 76117 items
600: 109501 items
700: 149019 items
800: 194751 items
900: 246327 items
1000: 304193 items

PARI/GP[edit]

Farey(n)=my(v=List()); for(k=1,n,for(i=0,k,listput(v,i/k))); vecsort(Set(v));
countFarey(n)=1+sum(k=1, n, eulerphi(k));
for(n=1,11,print(Farey(n)))
apply(countFarey, 100*[1..10])
Output:
[0, 1]
[0, 1/2, 1]
[0, 1/3, 1/2, 2/3, 1]
[0, 1/4, 1/3, 1/2, 2/3, 3/4, 1]
[0, 1/5, 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 1]
[0, 1/6, 1/5, 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 1]
[0, 1/7, 1/6, 1/5, 1/4, 2/7, 1/3, 2/5, 3/7, 1/2, 4/7, 3/5, 2/3, 5/7, 3/4, 4/5, 5/6, 6/7, 1]
[0, 1/8, 1/7, 1/6, 1/5, 1/4, 2/7, 1/3, 3/8, 2/5, 3/7, 1/2, 4/7, 3/5, 5/8, 2/3, 5/7, 3/4, 4/5, 5/6, 6/7, 7/8, 1]
[0, 1/9, 1/8, 1/7, 1/6, 1/5, 2/9, 1/4, 2/7, 1/3, 3/8, 2/5, 3/7, 4/9, 1/2, 5/9, 4/7, 3/5, 5/8, 2/3, 5/7, 3/4, 7/9, 4/5, 5/6, 6/7, 7/8, 8/9, 1]
[0, 1/10, 1/9, 1/8, 1/7, 1/6, 1/5, 2/9, 1/4, 2/7, 3/10, 1/3, 3/8, 2/5, 3/7, 4/9, 1/2, 5/9, 4/7, 3/5, 5/8, 2/3, 7/10, 5/7, 3/4, 7/9, 4/5, 5/6, 6/7, 7/8, 8/9, 9/10, 1]
[0, 1/11, 1/10, 1/9, 1/8, 1/7, 1/6, 2/11, 1/5, 2/9, 1/4, 3/11, 2/7, 3/10, 1/3, 4/11, 3/8, 2/5, 3/7, 4/9, 5/11, 1/2, 6/11, 5/9, 4/7, 3/5, 5/8, 7/11, 2/3, 7/10, 5/7, 8/11, 3/4, 7/9, 4/5, 9/11, 5/6, 6/7, 7/8, 8/9, 9/10, 10/11, 1]

%1 = [3045, 12233, 27399, 48679, 76117, 109501, 149019, 194751, 246327, 304193]

Pascal[edit]

Using a function, to get next in Farey sequence. calculated as stated in wikipedia article, see Lua [[2]]. So there is no need to store them in a big array..

program Farey;
{$IFDEF FPC }{$MODE DELPHI}{$ELSE}{$APPTYPE CONSOLE}{$ENDIF}
uses
sysutils;
type
tNextFarey= record
nom,dom,n,c,d: longInt;
end;
 
function InitFarey(maxdom:longINt):tNextFarey;
Begin
with result do
Begin
nom := 0; dom := 1; n := maxdom;
c := 1; d := maxdom;
end;
end;
 
function NextFarey(var fn:tNextFarey):boolean;
var
k,tmp: longInt;
Begin
with fn do
Begin
k := trunc((n + dom)/d);
tmp := c;c:= k*c-nom;nom:= tmp;
tmp := d;d:= k*d-dom;dom:= tmp;
result := nom <> dom;
end;
end;
 
var
TestF : tNextFarey;
cnt: NativeInt;
Begin
TestF:= InitFarey(10);
cnt := 1;// out of InitFarey
repeat
write(TestF.nom,'/',TestF.dom,',');
inc(cnt);
until NOT(NextFarey(TestF));
writeln(TestF.nom,'/',TestF.dom);
writeln(cnt);
 
TestF:= InitFarey(10000);
cnt := 1;
repeat
inc(cnt);
until NOT(NextFarey(TestF));
writeln(TestF.n:10,cnt:16);
end.
Output:
  0/1,1/10,1/9,1/8,1/7,1/6,1/5,2/9,1/4,2/7,3/10,1/3,3/8,2/5,3/7,4/9,1/2
 ,5/9,4/7,3/5,5/8,2/3,7/10,5/7,3/4,7/9,4/5,5/6,6/7,7/8,8/9,9/10,1/1
33
     10000        30397487

real    0m0.331s

Perl[edit]

Recurrence[edit]

This uses the recurrence from Concrete Mathematics exercise 4.61 to create them quickly (this is also on the Wikipedia page). It also uses the totient sum to quickly get the counts.

use warnings;
use strict;
use Math::BigRat;
use ntheory qw/euler_phi vecsum/;
 
sub farey {
my $N = shift;
my @f;
my($m0,$n0, $m1,$n1) = (0, 1, 1, $N);
push @f, Math::BigRat->new("$m0/$n0");
push @f, Math::BigRat->new("$m1/$n1");
while ($f[-1] < 1) {
my $m = int( ($n0 + $N) / $n1) * $m1 - $m0;
my $n = int( ($n0 + $N) / $n1) * $n1 - $n0;
($m0,$n0, $m1,$n1) = ($m1,$n1, $m,$n);
push @f, Math::BigRat->new("$m/$n");
}
@f;
}
sub farey_count { 1 + vecsum(euler_phi(1, shift)); }
 
for (1 .. 11) {
my @f = map { join "/", $_->parts } # Force 0/1 and 1/1
farey($_);
print "F$_: [@f]\n";
}
for (1 .. 10, 100000) {
print "F${_}00: ", farey_count(100*$_), " members\n";
}
Output:
F1: [0/1 1/1]
F2: [0/1 1/2 1/1]
F3: [0/1 1/3 1/2 2/3 1/1]
F4: [0/1 1/4 1/3 1/2 2/3 3/4 1/1]
F5: [0/1 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 1/1]
F6: [0/1 1/6 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 5/6 1/1]
F7: [0/1 1/7 1/6 1/5 1/4 2/7 1/3 2/5 3/7 1/2 4/7 3/5 2/3 5/7 3/4 4/5 5/6 6/7 1/1]
F8: [0/1 1/8 1/7 1/6 1/5 1/4 2/7 1/3 3/8 2/5 3/7 1/2 4/7 3/5 5/8 2/3 5/7 3/4 4/5 5/6 6/7 7/8 1/1]
F9: [0/1 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 1/1]
F10: [0/1 1/10 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 3/10 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 7/10 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 9/10 1/1]
F11: [0/1 1/11 1/10 1/9 1/8 1/7 1/6 2/11 1/5 2/9 1/4 3/11 2/7 3/10 1/3 4/11 3/8 2/5 3/7 4/9 5/11 1/2 6/11 5/9 4/7 3/5 5/8 7/11 2/3 7/10 5/7 8/11 3/4 7/9 4/5 9/11 5/6 6/7 7/8 8/9 9/10 10/11 1/1]
F100: 3045 members
F200: 12233 members
F300: 27399 members
F400: 48679 members
F500: 76117 members
F600: 109501 members
F700: 149019 members
F800: 194751 members
F900: 246327 members
F1000: 304193 members
F10000000: 30396356427243 members

Mapped Rationals[edit]

Similar to Pari and Perl6. Same output, quite slow. Using the recursive formula for the count, utilizing the Memoize module, would be a big help.

use warnings;
use strict;
use Math::BigRat;
 
sub farey {
my $n = shift;
my %v;
for my $k (1 .. $n) {
for my $i (0 .. $k) {
$v{ Math::BigRat->new("$i/$k")->bstr }++;
}
}
my @f = sort {$a <=> $b }
map { Math::BigRat->new($_) }
keys %v;
@f;
}
 
for (1 .. 11) {
my @f = map { join "/", $_->parts } # Force 0/1 and 1/1
farey($_);
print "F$_: [@f]\n";
}
for (1 .. 10) {
my @f = farey(100*$_);
print "F${_}00: ", scalar(@f), " members\n";
}

Perl 6[edit]

Works with: rakudo version 2016.05
sub farey ($order) {
my @l = 0/1;
(1..$order).map: { push @l, |(1..$^d).map: { $^n/$d } }
unique gather @l.deepmap(*.take);
}
 
say "Farey sequence order ";
say "$_: ", .&farey.sort.map: *.nude.join('/') for 1..11;
say "Farey sequence order $_ has ", [.&farey].elems, ' elements.' for 100, 200 ... 1000;
Output:
Farey sequence order 
1: 0/1 1/1
2: 0/1 1/2 1/1
3: 0/1 1/3 1/2 2/3 1/1
4: 0/1 1/4 1/3 1/2 2/3 3/4 1/1
5: 0/1 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 1/1
6: 0/1 1/6 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 5/6 1/1
7: 0/1 1/7 1/6 1/5 1/4 2/7 1/3 2/5 3/7 1/2 4/7 3/5 2/3 5/7 3/4 4/5 5/6 6/7 1/1
8: 0/1 1/8 1/7 1/6 1/5 1/4 2/7 1/3 3/8 2/5 3/7 1/2 4/7 3/5 5/8 2/3 5/7 3/4 4/5 5/6 6/7 7/8 1/1
9: 0/1 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 1/1
10: 0/1 1/10 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 3/10 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 7/10 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 9/10 1/1
11: 0/1 1/11 1/10 1/9 1/8 1/7 1/6 2/11 1/5 2/9 1/4 3/11 2/7 3/10 1/3 4/11 3/8 2/5 3/7 4/9 5/11 1/2 6/11 5/9 4/7 3/5 5/8 7/11 2/3 7/10 5/7 8/11 3/4 7/9 4/5 9/11 5/6 6/7 7/8 8/9 9/10 10/11 1/1
Farey sequence order 100 has 3045 elements.
Farey sequence order 200 has 12233 elements.
Farey sequence order 300 has 27399 elements.
Farey sequence order 400 has 48679 elements.
Farey sequence order 500 has 76117 elements.
Farey sequence order 600 has 109501 elements.
Farey sequence order 700 has 149019 elements.
Farey sequence order 800 has 194751 elements.
Farey sequence order 900 has 246327 elements.
Farey sequence order 1000 has 304193 elements.

Phix[edit]

Translation of: AWK
function farey(integer n)
integer a=0, b=1, c=1, d=n
integer items=1
if n<=11 then
printf(1,"%d: %d/%d",{n,a,b})
end if
while c<=n do
integer k = floor((n+b)/d)
{a,b,c,d} = {c,d,k*c-a,k*d-b}
items += 1
if n<=11 then
printf(1," %d/%d",{a,b})
end if
end while
return items
end function
 
printf(1,"Farey sequence for order 1 through 11:\n")
for i=1 to 11 do
{} = farey(i)
printf(1,"\n")
end for
printf(1,"Farey sequence fractions, 100 to 1000 by hundreds:\n")
sequence nf = {}
for i=100 to 1000 by 100 do
nf = append(nf,farey(i))
end for
?nf
Output:
Farey sequence for order 1 through 11:
1: 0/1 1/1
2: 0/1 1/2 1/1
3: 0/1 1/3 1/2 2/3 1/1
4: 0/1 1/4 1/3 1/2 2/3 3/4 1/1
5: 0/1 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 1/1
6: 0/1 1/6 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 5/6 1/1
7: 0/1 1/7 1/6 1/5 1/4 2/7 1/3 2/5 3/7 1/2 4/7 3/5 2/3 5/7 3/4 4/5 5/6 6/7 1/1
8: 0/1 1/8 1/7 1/6 1/5 1/4 2/7 1/3 3/8 2/5 3/7 1/2 4/7 3/5 5/8 2/3 5/7 3/4 4/5 5/6 6/7 7/8 1/1
9: 0/1 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 1/1
10: 0/1 1/10 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 3/10 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 7/10 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 9/10 1/1
11: 0/1 1/11 1/10 1/9 1/8 1/7 1/6 2/11 1/5 2/9 1/4 3/11 2/7 3/10 1/3 4/11 3/8 2/5 3/7 4/9 5/11 1/2 6/11 5/9 4/7 3/5 5/8 7/11 2/3 7/10 5/7 8/11 3/4 7/9 4/5 9/11 5/6 6/7 7/8 8/9 9/10 10/11 1/1
Farey sequence fractions, 100 to 1000 by hundreds:
{3045,12233,27399,48679,76117,109501,149019,194751,246327,304193}

Prolog[edit]

The following uses SWI-Prolog's rationals (rdiv(p,q)) and assumes the availability of predsort/3. The presentation is top-down.

task(1) :-
between(1, 11, I),
farey(I, F),
write(I), write(': '),
rwrite(F), nl, fail; true.
 
task(2) :- between(1, 10, I),
I100 is I*100,
farey( I100, F),
length(F,N),
write('|F('), write(I100), write(')| = '), writeln(N), fail; true.
 
% farey(+Order, Sequence)
farey(Order, Sequence) :-
bagof( R,
I^J^(between(1, Order, J), between(0, J, I), R is I rdiv J),
S),
predsort( rcompare, S, Sequence ).
 
rprint( rdiv(A,B) ) :- write(A), write(/), write(B), !.
rprint( I ) :- integer(I), write(I), write(/), write(1), !.
 
rwrite([]).
rwrite([R]) :- rprint(R).
rwrite([R, T|Rs]) :- rprint(R), write(', '), rwrite([T|Rs]).
 
rcompare(<, A, B) :- A < B, !.
rcompare(>, A, B) :- A > B, !.
rcompare(=, A, B) :- A =< B.
Interactive session:
?- task(1).
1: 0/1, 1/1
2: 0/1, 1/2, 1/1
3: 0/1, 1/3, 1/2, 2/3, 1/1
4: 0/1, 1/4, 1/3, 1/2, 2/3, 3/4, 1/1
5: 0/1, 1/5, 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 1/1
6: 0/1, 1/6, 1/5, 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 1/1
7: 0/1, 1/7, 1/6, 1/5, 1/4, 2/7, 1/3, 2/5, 3/7, 1/2, 4/7, 3/5, 2/3, 5/7, 3/4, 4/5, 5/6, 6/7, 1/1
8: 0/1, 1/8, 1/7, 1/6, 1/5, 1/4, 2/7, 1/3, 3/8, 2/5, 3/7, 1/2, 4/7, 3/5, 5/8, 2/3, 5/7, 3/4, 4/5, 5/6, 6/7, 7/8, 1/1
9: 0/1, 1/9, 1/8, 1/7, 1/6, 1/5, 2/9, 1/4, 2/7, 1/3, 3/8, 2/5, 3/7, 4/9, 1/2, 5/9, 4/7, 3/5, 5/8, 2/3, 5/7, 3/4, 7/9, 4/5, 5/6, 6/7, 7/8, 8/9, 1/1
10: 0/1, 1/10, 1/9, 1/8, 1/7, 1/6, 1/5, 2/9, 1/4, 2/7, 3/10, 1/3, 3/8, 2/5, 3/7, 4/9, 1/2, 5/9, 4/7, 3/5, 5/8, 2/3, 7/10, 5/7, 3/4, 7/9, 4/5, 5/6, 6/7, 7/8, 8/9, 9/10, 1/1
11: 0/1, 1/11, 1/10, 1/9, 1/8, 1/7, 1/6, 2/11, 1/5, 2/9, 1/4, 3/11, 2/7, 3/10, 1/3, 4/11, 3/8, 2/5, 3/7, 4/9, 5/11, 1/2, 6/11, 5/9, 4/7, 3/5, 5/8, 7/11, 2/3, 7/10, 5/7, 8/11, 3/4, 7/9, 4/5, 9/11, 5/6, 6/7, 7/8, 8/9, 9/10, 10/11, 1/1
true

?- task(2).
|F(100)| = 3045
|F(200)| = 12233
|F(300)| = 27399
|F(400)| = 48679
|F(500)| = 76117
|F(600)| = 109501
|F(700)| = 149019
|F(800)| = 194751
|F(900)| = 246327
|F(1000)| = 304193
true.

Python[edit]

from fractions import Fraction
 
 
class Fr(Fraction):
def __repr__(self):
return '(%s/%s)' % (self.numerator, self.denominator)
 
 
def farey(n, length=False):
if not length:
return [Fr(0, 1)] + sorted({Fr(m, k) for k in range(1, n+1) for m in range(1, k+1)})
else:
#return 1 + len({Fr(m, k) for k in range(1, n+1) for m in range(1, k+1)})
return (n*(n+3))//2 - sum(farey(n//k, True) for k in range(2, n+1))
 
if __name__ == '__main__':
print('Farey sequence for order 1 through 11 (inclusive):')
for n in range(1, 12):
print(farey(n))
print('Number of fractions in the Farey sequence for order 100 through 1,000 (inclusive) by hundreds:')
print([farey(i, length=True) for i in range(100, 1001, 100)])
Output:
Farey sequence for order 1 through 11 (inclusive):
[(0/1), (1/1)]
[(0/1), (1/2), (1/1)]
[(0/1), (1/3), (1/2), (2/3), (1/1)]
[(0/1), (1/4), (1/3), (1/2), (2/3), (3/4), (1/1)]
[(0/1), (1/5), (1/4), (1/3), (2/5), (1/2), (3/5), (2/3), (3/4), (4/5), (1/1)]
[(0/1), (1/6), (1/5), (1/4), (1/3), (2/5), (1/2), (3/5), (2/3), (3/4), (4/5), (5/6), (1/1)]
[(0/1), (1/7), (1/6), (1/5), (1/4), (2/7), (1/3), (2/5), (3/7), (1/2), (4/7), (3/5), (2/3), (5/7), (3/4), (4/5), (5/6), (6/7), (1/1)]
[(0/1), (1/8), (1/7), (1/6), (1/5), (1/4), (2/7), (1/3), (3/8), (2/5), (3/7), (1/2), (4/7), (3/5), (5/8), (2/3), (5/7), (3/4), (4/5), (5/6), (6/7), (7/8), (1/1)]
[(0/1), (1/9), (1/8), (1/7), (1/6), (1/5), (2/9), (1/4), (2/7), (1/3), (3/8), (2/5), (3/7), (4/9), (1/2), (5/9), (4/7), (3/5), (5/8), (2/3), (5/7), (3/4), (7/9), (4/5), (5/6), (6/7), (7/8), (8/9), (1/1)]
[(0/1), (1/10), (1/9), (1/8), (1/7), (1/6), (1/5), (2/9), (1/4), (2/7), (3/10), (1/3), (3/8), (2/5), (3/7), (4/9), (1/2), (5/9), (4/7), (3/5), (5/8), (2/3), (7/10), (5/7), (3/4), (7/9), (4/5), (5/6), (6/7), (7/8), (8/9), (9/10), (1/1)]
[(0/1), (1/11), (1/10), (1/9), (1/8), (1/7), (1/6), (2/11), (1/5), (2/9), (1/4), (3/11), (2/7), (3/10), (1/3), (4/11), (3/8), (2/5), (3/7), (4/9), (5/11), (1/2), (6/11), (5/9), (4/7), (3/5), (5/8), (7/11), (2/3), (7/10), (5/7), (8/11), (3/4), (7/9), (4/5), (9/11), (5/6), (6/7), (7/8), (8/9), (9/10), (10/11), (1/1)]
Number of fractions in the Farey sequence for order 100 through 1,000 (inclusive) by hundreds:
[3045, 12233, 27399, 48679, 76117, 109501, 149019, 194751, 246327, 304193]

Racket[edit]

Once again, racket's math/number-theory package comes to the rescue!

#lang racket
(require math/number-theory)
(define (display-farey-sequence order show-fractions?)
(define f-s (farey-sequence order))
(printf "-- Farey Sequence for order ~a has ~a fractions~%" order (length f-s))
 ;; racket will simplify 0/1 and 1/1 to 0 and 1 respectively, so deconstruct into numerator and
 ;; denomimator (and take the opportunity to insert commas
(when show-fractions?
(displayln
(string-join
(for/list ((f f-s))
(format "~a/~a" (numerator f) (denominator f)))
", "))))
 
; compute and show the Farey sequence for order:
; 1 through 11 (inclusive).
(for ((order (in-range 1 (add1 11)))) (display-farey-sequence order #t))
; compute and display the number of fractions in the Farey sequence for order:
; 100 through 1,000 (inclusive) by hundreds.
(for ((order (in-range 100 (add1 1000) 100))) (display-farey-sequence order #f))
Output:
-- Farey Sequence for order 1 has 2 fractions
0/1, 1/1
-- Farey Sequence for order 2 has 3 fractions
0/1, 1/2, 1/1
-- Farey Sequence for order 3 has 5 fractions
0/1, 1/3, 1/2, 2/3, 1/1
-- Farey Sequence for order 4 has 7 fractions
0/1, 1/4, 1/3, 1/2, 2/3, 3/4, 1/1
-- Farey Sequence for order 5 has 11 fractions
0/1, 1/5, 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 1/1
-- Farey Sequence for order 6 has 13 fractions
0/1, 1/6, 1/5, 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 1/1
-- Farey Sequence for order 7 has 19 fractions
0/1, 1/7, 1/6, 1/5, 1/4, 2/7, 1/3, 2/5, 3/7, 1/2, 4/7, 3/5, 2/3, 5/7, 3/4, 4/5, 5/6, 6/7, 1/1
-- Farey Sequence for order 8 has 23 fractions
0/1, 1/8, 1/7, 1/6, 1/5, 1/4, 2/7, 1/3, 3/8, 2/5, 3/7, 1/2, 4/7, 3/5, 5/8, 2/3, 5/7, 3/4, 4/5, 5/6, 6/7, 7/8, 1/1
-- Farey Sequence for order 9 has 29 fractions
0/1, 1/9, 1/8, 1/7, 1/6, 1/5, 2/9, 1/4, 2/7, 1/3, 3/8, 2/5, 3/7, 4/9, 1/2, 5/9, 4/7, 3/5, 5/8, 2/3, 5/7, 3/4, 7/9, 4/5, 5/6, 6/7, 7/8, 8/9, 1/1
-- Farey Sequence for order 10 has 33 fractions
0/1, 1/10, 1/9, 1/8, 1/7, 1/6, 1/5, 2/9, 1/4, 2/7, 3/10, 1/3, 3/8, 2/5, 3/7, 4/9, 1/2, 5/9, 4/7, 3/5, 5/8, 2/3, 7/10, 5/7, 3/4, 7/9, 4/5, 5/6, 6/7, 7/8, 8/9, 9/10, 1/1
-- Farey Sequence for order 11 has 43 fractions
0/1, 1/11, 1/10, 1/9, 1/8, 1/7, 1/6, 2/11, 1/5, 2/9, 1/4, 3/11, 2/7, 3/10, 1/3, 4/11, 3/8, 2/5, 3/7, 4/9, 5/11, 1/2, 6/11, 5/9, 4/7, 3/5, 5/8, 7/11, 2/3, 7/10, 5/7, 8/11, 3/4, 7/9, 4/5, 9/11, 5/6, 6/7, 7/8, 8/9, 9/10, 10/11, 1/1
-- Farey Sequence for order 100 has 3045 fractions
-- Farey Sequence for order 200 has 12233 fractions
-- Farey Sequence for order 300 has 27399 fractions
-- Farey Sequence for order 400 has 48679 fractions
-- Farey Sequence for order 500 has 76117 fractions
-- Farey Sequence for order 600 has 109501 fractions
-- Farey Sequence for order 700 has 149019 fractions
-- Farey Sequence for order 800 has 194751 fractions
-- Farey Sequence for order 900 has 246327 fractions
-- Farey Sequence for order 1000 has 304193 fractions

REXX[edit]

/*REXX program  computes and displays  a  Farey sequence  (or the number of fractions). */
parse arg L H I . /*obtain optional arguments from the CL*/
if L=='' | L=="," then L=5 /*Not specified? Then use the default.*/
oldL=L /*original L (negativity=no display.*/
L=abs(L) /*but ··· use │L│ for all else. */
if H=='' | H=="," then H=L /*Not specified? Then use the default.*/
if I=='' | I=="," then I=1 /* " " " " " " */
/*step through the range by increment. */
do n=L to H by I /*process the range (could be only one)*/
@=fareyF(n); #=' 'words(@)" " /*go ye forth and compute Farey numbers*/
say center('Farey sequence for order ' n " has" # 'fractions.', 150, "═")
if oldL<0 then iterate /*don't display Farey fractions if neg.*/
say @; say /*show Farey fractions and a blank line*/
end /*n*/ /* [↑] build/display Farey fractions. */
exit /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
fareyF: procedure; parse arg x; n.1=0; d.1=1; n.2=1; d.2=x /*some kit parts.*/
$=n.1'/'d.1 n.2"/"d.2 /*a starter kit for the Farey sequence.*/
/* [↓] now, build on the starter kit. */
do j=1; y=j+1; z=j+2 /*construct from thirds and on "up".*/
n.z= (d.j+x) % d.y*n.y - n.j /* " the fraction numerator. */
d.z= (d.j+x) % d.y*d.y - d.j /* " " " denominator. */
if n.z>x then leave /*Should the construction be stopped ? */
$=$ n.z'/'d.z /*Heck no, add fraction to party mix. */
end /*j*/ /* [↑] construct the Farey sequence. */
return $ /*return with the Farey fractions. */

output   when using the following for input:     1   11

═══════════════════════════════════════════════════Farey sequence for order  1  has  2  fractions.════════════════════════════════════════════════════
0/1 1/1

═══════════════════════════════════════════════════Farey sequence for order  2  has  3  fractions.════════════════════════════════════════════════════
0/1 1/2 1/1

═══════════════════════════════════════════════════Farey sequence for order  3  has  5  fractions.════════════════════════════════════════════════════
0/1 1/3 1/2 2/3 1/1

═══════════════════════════════════════════════════Farey sequence for order  4  has  7  fractions.════════════════════════════════════════════════════
0/1 1/4 1/3 1/2 2/3 3/4 1/1

═══════════════════════════════════════════════════Farey sequence for order  5  has  11  fractions.═══════════════════════════════════════════════════
0/1 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 1/1

═══════════════════════════════════════════════════Farey sequence for order  6  has  13  fractions.═══════════════════════════════════════════════════
0/1 1/6 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 5/6 1/1

═══════════════════════════════════════════════════Farey sequence for order  7  has  19  fractions.═══════════════════════════════════════════════════
0/1 1/7 1/6 1/5 1/4 2/7 1/3 2/5 3/7 1/2 4/7 3/5 2/3 5/7 3/4 4/5 5/6 6/7 1/1

═══════════════════════════════════════════════════Farey sequence for order  8  has  23  fractions.═══════════════════════════════════════════════════
0/1 1/8 1/7 1/6 1/5 1/4 2/7 1/3 3/8 2/5 3/7 1/2 4/7 3/5 5/8 2/3 5/7 3/4 4/5 5/6 6/7 7/8 1/1

═══════════════════════════════════════════════════Farey sequence for order  9  has  29  fractions.═══════════════════════════════════════════════════
0/1 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 1/1

══════════════════════════════════════════════════Farey sequence for order  10  has  33  fractions.═══════════════════════════════════════════════════
0/1 1/10 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 3/10 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 7/10 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 9/10 1/1

══════════════════════════════════════════════════Farey sequence for order  11  has  43  fractions.═══════════════════════════════════════════════════
0/1 1/11 1/10 1/9 1/8 1/7 1/6 2/11 1/5 2/9 1/4 3/11 2/7 3/10 1/3 4/11 3/8 2/5 3/7 4/9 5/11 1/2 6/11 5/9 4/7 3/5 5/8 7/11 2/3 7/10 5/7 8/11 3/4 7/9 4/5 9/11 5/6 6/7 7/8 8/9 9/10 10/11 1/1

output   when using the following for input:     -100   1000   100

═════════════════════════════════════════════════Farey sequence for order  100  has  3045  fractions.═════════════════════════════════════════════════
════════════════════════════════════════════════Farey sequence for order  200  has  12233  fractions.═════════════════════════════════════════════════
════════════════════════════════════════════════Farey sequence for order  300  has  27399  fractions.═════════════════════════════════════════════════
════════════════════════════════════════════════Farey sequence for order  400  has  48679  fractions.═════════════════════════════════════════════════
════════════════════════════════════════════════Farey sequence for order  500  has  76117  fractions.═════════════════════════════════════════════════
════════════════════════════════════════════════Farey sequence for order  600  has  109501  fractions.════════════════════════════════════════════════
════════════════════════════════════════════════Farey sequence for order  700  has  149019  fractions.════════════════════════════════════════════════
════════════════════════════════════════════════Farey sequence for order  800  has  194751  fractions.════════════════════════════════════════════════
════════════════════════════════════════════════Farey sequence for order  900  has  246327  fractions.════════════════════════════════════════════════
═══════════════════════════════════════════════Farey sequence for order  1000  has  304193  fractions.════════════════════════════════════════════════

Ruby[edit]

Translation of: Python
def farey(n, length=false)
if length
(n*(n+3))/2 - (2..n).inject(0){|sum,k| sum + farey(n/k, true)}
else
(1..n).each_with_object([]){|k,a|(0..k).each{|m|a << Rational(m,k)}}.uniq.sort
end
end
 
puts 'Farey sequence for order 1 through 11 (inclusive):'
for n in 1..11
puts "F(#{n}): " + farey(n).join(", ")
end
puts 'Number of fractions in the Farey sequence:'
for i in (100..1000).step(100)
puts "F(%4d) =%7d" % [i, farey(i, true)]
end
Output:
Farey sequence for order 1 through 11 (inclusive):
F(1): 0/1, 1/1
F(2): 0/1, 1/2, 1/1
F(3): 0/1, 1/3, 1/2, 2/3, 1/1
F(4): 0/1, 1/4, 1/3, 1/2, 2/3, 3/4, 1/1
F(5): 0/1, 1/5, 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 1/1
F(6): 0/1, 1/6, 1/5, 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 1/1
F(7): 0/1, 1/7, 1/6, 1/5, 1/4, 2/7, 1/3, 2/5, 3/7, 1/2, 4/7, 3/5, 2/3, 5/7, 3/4, 4/5, 5/6, 6/7, 1/1
F(8): 0/1, 1/8, 1/7, 1/6, 1/5, 1/4, 2/7, 1/3, 3/8, 2/5, 3/7, 1/2, 4/7, 3/5, 5/8, 2/3, 5/7, 3/4, 4/5, 5/6, 6/7, 7/8, 1/1
F(9): 0/1, 1/9, 1/8, 1/7, 1/6, 1/5, 2/9, 1/4, 2/7, 1/3, 3/8, 2/5, 3/7, 4/9, 1/2, 5/9, 4/7, 3/5, 5/8, 2/3, 5/7, 3/4, 7/9, 4/5, 5/6, 6/7, 7/8, 8/9, 1/1
F(10): 0/1, 1/10, 1/9, 1/8, 1/7, 1/6, 1/5, 2/9, 1/4, 2/7, 3/10, 1/3, 3/8, 2/5, 3/7, 4/9, 1/2, 5/9, 4/7, 3/5, 5/8, 2/3, 7/10, 5/7, 3/4, 7/9, 4/5, 5/6, 6/7, 7/8, 8/9, 9/10, 1/1
F(11): 0/1, 1/11, 1/10, 1/9, 1/8, 1/7, 1/6, 2/11, 1/5, 2/9, 1/4, 3/11, 2/7, 3/10, 1/3, 4/11, 3/8, 2/5, 3/7, 4/9, 5/11, 1/2, 6/11, 5/9, 4/7, 3/5, 5/8, 7/11, 2/3, 7/10, 5/7, 8/11, 3/4, 7/9, 4/5, 9/11, 5/6, 6/7, 7/8, 8/9, 9/10, 10/11, 1/1
Number of fractions in the Farey sequence:
F( 100) =   3045
F( 200) =  12233
F( 300) =  27399
F( 400) =  48679
F( 500) =  76117
F( 600) = 109501
F( 700) = 149019
F( 800) = 194751
F( 900) = 246327
F(1000) = 304193


Scala[edit]

This example is incomplete. Part 2 of the task is not implemented here. Please ensure that it meets all task requirements and remove this message.
def FareySequence(n: Int, start: (Int, Int)=(0, 1), stop: (Int, Int)=(1, 1)): Stream[(Int, Int)] = {
val (nominator_l, denominator_l) = start
val (nominator_r, denominator_r) = stop
 
val mediant = ((nominator_l + nominator_r), (denominator_l + denominator_r))
 
if (mediant._2 <= n) FareySequence(n, start, mediant) ++ mediant #:: FareySequence(n, mediant, stop)
else Stream.empty
}
 
for (i <- 1 to 11) {
println(FareySequence(i).map((a, b) => s"$a/$b").mkString(", "))
}
Output:

1/2
1/3, 1/2, 2/3
1/4, 1/3, 1/2, 2/3, 3/4
1/5, 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5
1/6, 1/5, 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6
1/7, 1/6, 1/5, 1/4, 2/7, 1/3, 2/5, 3/7, 1/2, 4/7, 3/5, 2/3, 5/7, 3/4, 4/5, 5/6, 6/7
1/8, 1/7, 1/6, 1/5, 1/4, 2/7, 1/3, 3/8, 2/5, 3/7, 1/2, 4/7, 3/5, 5/8, 2/3, 5/7, 3/4, 4/5, 5/6, 6/7, 7/8
1/9, 1/8, 1/7, 1/6, 1/5, 2/9, 1/4, 2/7, 1/3, 3/8, 2/5, 3/7, 4/9, 1/2, 5/9, 4/7, 3/5, 5/8, 2/3, 5/7, 3/4, 7/9, 4/5, 5/6, 6/7, 7/8, 8/9
1/10, 1/9, 1/8, 1/7, 1/6, 1/5, 2/9, 1/4, 2/7, 3/10, 1/3, 3/8, 2/5, 3/7, 4/9, 1/2, 5/9, 4/7, 3/5, 5/8, 2/3, 7/10, 5/7, 3/4, 7/9, 4/5, 5/6, 6/7, 7/8, 8/9, 9/10
1/11, 1/10, 1/9, 1/8, 1/7, 1/6, 2/11, 1/5, 2/9, 1/4, 3/11, 2/7, 3/10, 1/3, 4/11, 3/8, 2/5, 3/7, 4/9, 5/11, 1/2, 6/11, 5/9, 4/7, 3/5, 5/8, 7/11, 2/3, 7/10, 5/7, 8/11, 3/4, 7/9, 4/5, 9/11, 5/6, 6/7, 7/8, 8/9, 9/10, 10/11

Scheme[edit]

 
(import (scheme base)
(scheme write))
 
;; create a generator for Farey sequence n
;; using next term formula from https://en.wikipedia.org/wiki/Farey_sequence
(define (farey-generator n)
(let ((a #f) (b 1) (c #f) (d n))
(lambda ()
(cond ((not a) ; first item in sequence
(set! a 0)
(/ a b))
((not c) ; second item in sequence
(set! c 1)
(/ c d))
((= c d) ; return #f when finished sequence
#f)
(else ; compute next term
(let* ((f (floor (/ (+ n b) d)))
(p (- (* f c) a))
(q (- (* f d) b)))
(set! a c)
(set! b d)
(set! c p)
(set! d q)
(/ p q)))))))
 
(define (farey-sequence n display?)
(define (display-rat n) ; ensure 0,1 show /1
(display n)
(when (= 1 (denominator n))
(display "/1"))
(display " "))
;
(let ((gen (farey-generator n)))
(do ((res (gen) (gen))
(count 0 (+ 1 count)))
((not res) (when display? (newline))
count)
(when display? (display-rat res)))))
 
;;
 
(display "Farey sequence for order 1 through 11 (inclusive):\n")
(do ((i 1 (+ i 1)))
((> i 11) )
(display (string-append "F(" (number->string i) "): "))
(farey-sequence i #t))
 
(display "\nNumber of fractions in the Farey sequence:\n")
(do ((i 100 (+ i 100)))
((> i 1000) )
(display
(string-append "F(" (number->string i) ") = "
(number->string (farey-sequence i #f))))
(newline))
 
Output:
Farey sequence for order 1 through 11 (inclusive):
F(1): 0/1 1/1 
F(2): 0/1 1/2 1/1 
F(3): 0/1 1/3 1/2 2/3 1/1 
F(4): 0/1 1/4 1/3 1/2 2/3 3/4 1/1 
F(5): 0/1 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 1/1 
F(6): 0/1 1/6 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 5/6 1/1 
F(7): 0/1 1/7 1/6 1/5 1/4 2/7 1/3 2/5 3/7 1/2 4/7 3/5 2/3 5/7 3/4 4/5 5/6 6/7 1/1 
F(8): 0/1 1/8 1/7 1/6 1/5 1/4 2/7 1/3 3/8 2/5 3/7 1/2 4/7 3/5 5/8 2/3 5/7 3/4 4/5 5/6 6/7 7/8 1/1 
F(9): 0/1 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 1/1 
F(10): 0/1 1/10 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 3/10 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 7/10 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 9/10 1/1 
F(11): 0/1 1/11 1/10 1/9 1/8 1/7 1/6 2/11 1/5 2/9 1/4 3/11 2/7 3/10 1/3 4/11 3/8 2/5 3/7 4/9 5/11 1/2 6/11 5/9 4/7 3/5 5/8 7/11 2/3 7/10 5/7 8/11 3/4 7/9 4/5 9/11 5/6 6/7 7/8 8/9 9/10 10/11 1/1 

Number of fractions in the Farey sequence:
F(100) = 3045
F(200) = 12233
F(300) = 27399
F(400) = 48679
F(500) = 76117
F(600) = 109501
F(700) = 149019
F(800) = 194751
F(900) = 246327
F(1000) = 304193

Sidef[edit]

Translation of: Ruby
func farey_count(n) {
(n*(n+3))//2 - (2..n -> sum_by {|k| farey_count(n//k) })
}
 
func farey(n) {
gather {
1..n -> each {|k| 0..k -> each {|m| take(m/k) }}
}.uniq.sort
}
 
say 'Farey sequence for order 1 through 11 (inclusive):'
for n in (1..11) {
say("F(%2d): %s" % (n, farey(n).map{.as_frac}.join(", ")))
}
 
say 'Number of fractions in the Farey sequence:'
for i in (100..1000 -> by(100)) {
say ("F(%4d) =%7d" % (i, farey_count(i)))
}
Output:
Farey sequence for order 1 through 11 (inclusive):
F( 1): 0/1, 1/1
F( 2): 0/1, 1/2, 1/1
F( 3): 0/1, 1/3, 1/2, 2/3, 1/1
F( 4): 0/1, 1/4, 1/3, 1/2, 2/3, 3/4, 1/1
F( 5): 0/1, 1/5, 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 1/1
F( 6): 0/1, 1/6, 1/5, 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 1/1
F( 7): 0/1, 1/7, 1/6, 1/5, 1/4, 2/7, 1/3, 2/5, 3/7, 1/2, 4/7, 3/5, 2/3, 5/7, 3/4, 4/5, 5/6, 6/7, 1/1
F( 8): 0/1, 1/8, 1/7, 1/6, 1/5, 1/4, 2/7, 1/3, 3/8, 2/5, 3/7, 1/2, 4/7, 3/5, 5/8, 2/3, 5/7, 3/4, 4/5, 5/6, 6/7, 7/8, 1/1
F( 9): 0/1, 1/9, 1/8, 1/7, 1/6, 1/5, 2/9, 1/4, 2/7, 1/3, 3/8, 2/5, 3/7, 4/9, 1/2, 5/9, 4/7, 3/5, 5/8, 2/3, 5/7, 3/4, 7/9, 4/5, 5/6, 6/7, 7/8, 8/9, 1/1
F(10): 0/1, 1/10, 1/9, 1/8, 1/7, 1/6, 1/5, 2/9, 1/4, 2/7, 3/10, 1/3, 3/8, 2/5, 3/7, 4/9, 1/2, 5/9, 4/7, 3/5, 5/8, 2/3, 7/10, 5/7, 3/4, 7/9, 4/5, 5/6, 6/7, 7/8, 8/9, 9/10, 1/1
F(11): 0/1, 1/11, 1/10, 1/9, 1/8, 1/7, 1/6, 2/11, 1/5, 2/9, 1/4, 3/11, 2/7, 3/10, 1/3, 4/11, 3/8, 2/5, 3/7, 4/9, 5/11, 1/2, 6/11, 5/9, 4/7, 3/5, 5/8, 7/11, 2/3, 7/10, 5/7, 8/11, 3/4, 7/9, 4/5, 9/11, 5/6, 6/7, 7/8, 8/9, 9/10, 10/11, 1/1
Number of fractions in the Farey sequence:
F( 100) =   3045
F( 200) =  12233
F( 300) =  27399
F( 400) =  48679
F( 500) =  76117
F( 600) = 109501
F( 700) = 149019
F( 800) = 194751
F( 900) = 246327
F(1000) = 304193

Swift[edit]

Class with computed properties:

class Farey {
let n: Int
 
init(_ x: Int) {
n = x
}
 
//using algorithm from wikipedia
var sequence: [(Int,Int)] {
var a = 0
var b = 1
var c = 1
var d = n
var results = [(a, b)]
while c <= n {
let k = (n + b) / d
let oldA = a
let oldB = b
a = c
b = d
c = k * c - oldA
d = k * d - oldB
results += [(a, b)]
}
return results
}
 
var formattedSequence: String {
var s = "\(n):"
for pair in sequence {
s += " \(pair.0)/\(pair.1)"
}
return s
}
 
}
 
print("Sequences\n")
 
for n in 1...11 {
print(Farey(n).formattedSequence)
}
 
print("\nSequence Lengths\n")
 
for n in 1...10 {
let m = n * 100
print("\(m): \(Farey(m).sequence.count)")
}
Output:
Sequences

1: 0/1 1/1
2: 0/1 1/2 1/1
3: 0/1 1/3 1/2 2/3 1/1
4: 0/1 1/4 1/3 1/2 2/3 3/4 1/1
5: 0/1 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 1/1
6: 0/1 1/6 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 5/6 1/1
7: 0/1 1/7 1/6 1/5 1/4 2/7 1/3 2/5 3/7 1/2 4/7 3/5 2/3 5/7 3/4 4/5 5/6 6/7 1/1
8: 0/1 1/8 1/7 1/6 1/5 1/4 2/7 1/3 3/8 2/5 3/7 1/2 4/7 3/5 5/8 2/3 5/7 3/4 4/5 5/6 6/7 7/8 1/1
9: 0/1 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 1/1
10: 0/1 1/10 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 3/10 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 7/10 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 9/10 1/1
11: 0/1 1/11 1/10 1/9 1/8 1/7 1/6 2/11 1/5 2/9 1/4 3/11 2/7 3/10 1/3 4/11 3/8 2/5 3/7 4/9 5/11 1/2 6/11 5/9 4/7 3/5 5/8 7/11 2/3 7/10 5/7 8/11 3/4 7/9 4/5 9/11 5/6 6/7 7/8 8/9 9/10 10/11 1/1

Sequence Lengths

100: 3045
200: 12233
300: 27399
400: 48679
500: 76117
600: 109501
700: 149019
800: 194751
900: 246327
1000: 304193

Tcl[edit]

Works with: Tcl version 8.6
package require Tcl 8.6
 
proc farey {n} {
set nums [lrepeat [expr {$n+1}] 1]
set result {{0 1}}
for {set found 1} {$found} {} {
set nj [lindex $nums [set j 1]]
for {set found 0;set i 1} {$i <= $n} {incr i} {
if {[lindex $nums $i]*$j < $nj*$i} {
set nj [lindex $nums [set j $i]]
set found 1
}
}
lappend result [list $nj $j]
for {set i $j} {$i <= $n} {incr i $j} {
lset nums $i [expr {[lindex $nums $i] + 1}]
}
}
return $result
}
 
for {set i 1} {$i <= 11} {incr i} {
puts F($i):\x20[lmap n [farey $i] {join $n /}]
}
for {set i 100} {$i <= 1000} {incr i 100} {
puts |F($i)|\x20=\x20[llength [farey $i]]
}
Output:
F(1): 0/1 1/1
F(2): 0/1 1/2 1/1
F(3): 0/1 1/3 1/2 2/3 1/1
F(4): 0/1 1/4 1/3 1/2 2/3 3/4 1/1
F(5): 0/1 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 1/1
F(6): 0/1 1/6 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 5/6 1/1
F(7): 0/1 1/7 1/6 1/5 1/4 2/7 1/3 2/5 3/7 1/2 4/7 3/5 2/3 5/7 3/4 4/5 5/6 6/7 1/1
F(8): 0/1 1/8 1/7 1/6 1/5 1/4 2/7 1/3 3/8 2/5 3/7 1/2 4/7 3/5 5/8 2/3 5/7 3/4 4/5 5/6 6/7 7/8 1/1
F(9): 0/1 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 1/1
F(10): 0/1 1/10 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 3/10 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 7/10 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 9/10 1/1
F(11): 0/1 1/11 1/10 1/9 1/8 1/7 1/6 2/11 1/5 2/9 1/4 3/11 2/7 3/10 1/3 4/11 3/8 2/5 3/7 4/9 5/11 1/2 6/11 5/9 4/7 3/5 5/8 7/11 2/3 7/10 5/7 8/11 3/4 7/9 4/5 9/11 5/6 6/7 7/8 8/9 9/10 10/11 1/1
|F(100)| = 3045
|F(200)| = 12233
|F(300)| = 27399
|F(400)| = 48679
|F(500)| = 76117
|F(600)| = 109501
|F(700)| = 149019
|F(800)| = 194751
|F(900)| = 246327
|F(1000)| = 304193

zkl[edit]

Translation of: C
fcn farey(n){
f1,f2:=T(0,1),T(1,n); // fraction is (num,dnom)
print("%d/%d %d/%d".fmt(0,1,1,n));
while(f2[1]>1){
k,t  :=(n + f1[1])/f2[1], f1;
f1,f2 = f2,T(f2[0]*k - t[0], f2[1]*k - t[1]);
print(" %d/%d".fmt(f2.xplode()));
}
println();
}
foreach n in ([1..11]){ print("%2d: ".fmt(n)); farey(n); }
Output:
 1: 0/1 1/1
 2: 0/1 1/2 1/1
 3: 0/1 1/3 1/2 2/3 1/1
 4: 0/1 1/4 1/3 1/2 2/3 3/4 1/1
 5: 0/1 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 1/1
 6: 0/1 1/6 1/5 1/4 1/3 2/5 1/2 3/5 2/3 3/4 4/5 5/6 1/1
 7: 0/1 1/7 1/6 1/5 1/4 2/7 1/3 2/5 3/7 1/2 4/7 3/5 2/3 5/7 3/4 4/5 5/6 6/7 1/1
 8: 0/1 1/8 1/7 1/6 1/5 1/4 2/7 1/3 3/8 2/5 3/7 1/2 4/7 3/5 5/8 2/3 5/7 3/4 4/5 5/6 6/7 7/8 1/1
 9: 0/1 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 1/1
10: 0/1 1/10 1/9 1/8 1/7 1/6 1/5 2/9 1/4 2/7 3/10 1/3 3/8 2/5 3/7 4/9 1/2 5/9 4/7 3/5 5/8 2/3 7/10 5/7 3/4 7/9 4/5 5/6 6/7 7/8 8/9 9/10 1/1
11: 0/1 1/11 1/10 1/9 1/8 1/7 1/6 2/11 1/5 2/9 1/4 3/11 2/7 3/10 1/3 4/11 3/8 2/5 3/7 4/9 5/11 1/2 6/11 5/9 4/7 3/5 5/8 7/11 2/3 7/10 5/7 8/11 3/4 7/9 4/5 9/11 5/6 6/7 7/8 8/9 9/10 10/11 1/1
fcn farey_len(n){
var cache=Dictionary(); // 107 keys to 1,000; [email protected],000,000
if(z:=cache.find(n)) return(z);
 
len,p,q := n*(n + 3)/2, 2,0;
while(p<=n){
q=n/(n/p) + 1;
len-=self.fcn(n/p) * (q - p);
p=q;
}
cache[n]=len; // len is returned
}
foreach n in ([100..1000,100]){ 
println("%4d: %7,d items".fmt(n,farey_len(n)));
}
n:=0d10_000_000;
println("\n%,d: %,d items".fmt(n,farey_len(n)));
Output:
 100:   3,045 items
 200:  12,233 items
 300:  27,399 items
 400:  48,679 items
 500:  76,117 items
 600: 109,501 items
 700: 149,019 items
 800: 194,751 items
 900: 246,327 items
1000: 304,193 items

10,000,000: 30,396,356,427,243 items