Lucas-Lehmer test
From Rosetta Code
You are encouraged to solve this task according to the task description, using any language you may know.
Lucas-Lehmer Test: for p a prime, the Mersenne number 2p − 1 is prime if and only if 2p − 1 divides S(p − 1) where S(n + 1) = (S(n))2 − 2, and S(1) = 4.
The following programs calculate all Mersenne primes up to the implementation's maximum precision, or the 47th Mersenne prime. (Which ever comes first).
Contents |
[edit] Ada
with Ada.Text_Io; use Ada.Text_Io;
with Ada.Integer_Text_Io; use Ada.Integer_Text_Io;
procedure Lucas_Lehmer_Test is
type Ull is mod 2**64;
function Mersenne(Item : Integer) return Boolean is
S : Ull := 4;
MP : Ull := 2**Item - 1;
begin
if Item = 2 then
return True;
else
for I in 3..Item loop
S := (S * S - 2) mod MP;
end loop;
return S = 0;
end if;
end Mersenne;
Upper_Bound : constant Integer := 64;
begin
Put_Line(" Mersenne primes:");
for P in 2..Upper_Bound loop
if Mersenne(P) then
Put(" M");
Put(Item => P, Width => 1);
end if;
end loop;
end Lucas_Lehmer_Test;
Output:
Mersenne primes: M2 M3 M5 M7 M13 M17 M19 M31
[edit] Agena
Because of the very large numbers computed, the mapm binding is used to calculate with arbitrary precision.
readlib 'mapm';
mapm.xdigits(100);
mersenne := proc(p::number) is
local s, m;
s := 4;
m := mapm.xnumber(2^p) - 1;
if p = 2 then
return true
else
for i from 3 to p do
s := (mapm.xnumber(s)^2 - 2) % m
od;
return mapm.xtoNumber(s) = 0
fi
end;
for i from 3 to 64 do
if mersenne(i) then
write('M' & i & ' ')
fi
od;
produces:
M3 M5 M7 M13 M17 M19 M31
[edit] ALGOL 68
Works with: ALGOL 68 version Revision 1 - no extensions to language used
Works with: ALGOL 68G version Any - tested with release 1.18.0-9h.tiny
PRAGMAT stack=1M precision=20000 PRAGMAT
PROC is prime = ( INT p )BOOL:
IF p = 2 THEN TRUE
ELIF p <= 1 OR p MOD 2 = 0 THEN FALSE
ELSE
BOOL prime := TRUE;
FOR i FROM 3 BY 2 TO ENTIER sqrt(p)
WHILE prime := p MOD i /= 0 DO SKIP OD;
prime
FI;
PROC is mersenne prime = ( INT p )BOOL:
IF p = 2 THEN TRUE
ELSE
LONG LONG INT m p := LONG LONG 2 ** p - 1, s := 4;
FROM 3 TO p DO
s := (s ** 2 - 2) MOD m p
OD;
s = 0
FI;
test:(
INT upb prime = ( long long bits width - 1 ) OVER 2; # no unsigned #
INT upb count = 45; # find 45 mprimes if INT has enough bits #
printf(($" Finding Mersenne primes in M[2.."g(0)"]: "l$,upb prime));
INT count:=0;
FOR p FROM 2 TO upb prime WHILE
IF is prime(p) THEN
IF is mersenne prime(p) THEN
printf (($" M"g(0)$,p));
count +:= 1
FI
FI;
count <= upb count
DO SKIP OD
)
Output:
Finding Mersenne primes in M[2..33252]: M2 M3 M5 M7 M13 M17 M19 M31 M61 M89 M107 M127 M521 M607 M1279 M2203 M2281 M3217 M4253 M4423 M9689 M9941 M11213 M19937 M21701 M23209
See also: http://www.xs4all.nl/~jmvdveer/mersenne.a68.html
[edit] C
Works with: gcc version 4.1.2 20070925 (Red Hat 4.1.2-27)
Works with: C99
Compiler options: gcc -std=c99 -lm Lucas-Lehmer_test.c -o Lucas-Lehmer_test
#include <math.h>
#include <stdio.h>
#include <limits.h>
#pragma precision=log10l(ULLONG_MAX)/2
typedef enum { FALSE=0, TRUE=1 } BOOL;
BOOL is_prime( int p ){
if( p == 2 ) return TRUE;
else if( p <= 1 || p % 2 == 0 ) return FALSE;
else {
BOOL prime = TRUE;
const int to = sqrt(p);
int i;
for(i = 3; i <= to; i+=2)
if (!(prime = p % i))break;
return prime;
}
}
BOOL is_mersenne_prime( int p ){
if( p == 2 ) return TRUE;
else {
const long long unsigned m_p = ( 1LLU << p ) - 1;
long long unsigned s = 4;
int i;
for (i = 3; i <= p; i++){
s = (s * s - 2) % m_p;
}
return s == 0;
}
}
int main(int argc, char **argv){
const int upb = log2l(ULLONG_MAX)/2;
int p;
printf(" Mersenne primes:\n");
for( p = 2; p <= upb; p += 1 ){
if( is_prime(p) && is_mersenne_prime(p) ){
printf (" M%u",p);
}
}
printf("\n");
}
Output:
Mersenne primes: M2 M3 M5 M7 M13 M17 M19 M31
[edit] C++
Library: GMP
#include <iostream>
#include <gmpxx.h>
mpz_class pow2(mpz_class exp);
bool is_mersenne_prime(mpz_class p);
int main()
{
mpz_class maxcount(45);
mpz_class found(0);
mpz_class check(0);
for( mpz_nextprime(check.get_mpz_t(), check.get_mpz_t());
found < maxcount;
mpz_nextprime(check.get_mpz_t(), check.get_mpz_t()))
{
//std::cout << "P" << check << " " << std::flush;
if( is_mersenne_prime(check) )
{
++found;
std::cout << "M" << check << " " << std::flush;
}
}
}
bool is_mersenne_prime(mpz_class p)
{
if( 2 == p )
return true;
else
{
mpz_class div = pow2(p) - mpz_class(1);
mpz_class s(4);
mpz_class s(4);
for( mpz_class i(3);
i <= p;
++i )
{
s = (s * s - mpz_class(2)) % div ;
}
return ( s == mpz_class(0) );
}
}
mpz_class pow2(mpz_class exp)
{
// Unfortunately, GMP doesn't have a left-shift method.
// It also doesn't have a pow() equivalent that takes arbitrary-precision exponents.
// So we have to do it the hard (and presumably slow) way.
mpz_class ret(2);
mpz_class ret(2);
for(mpz_class i(1); i < exp; ++i)
ret *= mpz_class(2);
ret *= mpz_class(2);
//std::cout << "pow2( " << exp << " ) = " << ret << std::endl;
return ret;
}
Output: (Incomplete; It takes a long time.)
M2 M3 M5 M7 M13 M17 M19 M31 M61 M89 M107 M127 M521 M607 M1279 M2203 M2281 M3217 M4253 M4423 M9689 M9941 M11213 M19937 M21701 M23209 M44497
[edit] Clojure
(defn prime? [i]
(cond (< i 4) (>= i 2)
(zero? (rem i 2)) false
:else (not-any? #(zero? (rem i %)) (range 3 (inc (Math/sqrt i))))))))
(defn mersenne? [p] (or (= p 2)
(let [mp (dec (bit-shift-left 1 p))]
(loop [n 3 s 4]
(if (> n p)
(zero? s)
(recur (inc n) (rem (- (* s s) 2) mp)))))))
(filter mersenne? (filter prime? (iterate inc 1)))
Output:
Infinite list of Mersenne primes: (2 3 5 7 13 17 19 31 61 89 107 127 521 607 1279 2203 2281 3217 4253...
[edit] Erlang
-module(mp).
-export([main/0]).
main() -> [ io:format("M~p ", [P]) || P <- lists:seq(2,700), (P == 2) orelse (s((1 bsl P) - 1, P-1) == 0) ].
s(MP,1) -> 4 rem MP;
s(MP,N) -> X=s(MP,N-1), (X*X - 2) rem MP.
In 3 seconds will print
M2 M3 M5 M7 M13 M17 M19 M31 M61 M89 M107 M127 M521 M607
Testing larger numbers (i.e. 5000) is possible but will take few minutes.
[edit] F#
Simple arbitrary-precision version:
let rec s mp n =
if n = 1 then 4I % mp else ((s mp (n - 1)) ** 2 - 2I) % mp
[ for p in 2..47 do
if p = 2 || s ((1I <<< p) - 1I) (p - 1) = 0I then
yield p ]
[edit] Fortran
Works with: Fortran version 90 and later Only Mersenne number with prime exponent can be themselves prime but for the small numbers used in this example it was not worth the effort to include this check. As the size of the exponent increases this becomes more important.
PROGRAM LUCAS_LEHMER
IMPLICIT NONE
INTEGER, PARAMETER :: i64 = SELECTED_INT_KIND(18)
INTEGER(i64) :: s, n
INTEGER :: i, exponent
DO exponent = 2, 31
IF (exponent == 2) THEN
s = 0
ELSE
s = 4
END IF
n = 2_i64**exponent - 1
DO i = 1, exponent-2
s = MOD(s*s - 2, n)
END DO
IF (s==0) WRITE(*,"(A,I0,A)") "M", exponent, " is PRIME"
END DO
END PROGRAM LUCAS_LEHMER
[edit] Haskell
Works with: GHCi version 6.8.2 Works with: GHC version 6.8.2
module Main
where
main = printMersennes $ take 45 $ filter lucasLehmer $ sieve [2..]
s mp 1 = 4 `mod` mp
s mp n = ((s mp $ n-1)^2-2) `mod` mp
lucasLehmer 2 = True
lucasLehmer p = s (2^p-1) (p-1) == 0
printMersennes = mapM_ (\x -> putStrLn $ "M" ++ show x)
It is pointed out on the Sieve of Eratosthenes page that the following "sieve" is inefficient. Nonetheless it takes very little time compared to the Lucas-Lehmer test itself.
sieve (p:xs) = p : sieve [x | x <- xs, x `mod` p > 0]
It takes about 30 minutes to get up to:
M2 M3 M5 M7 M13 M17 M19 M31 M61 M89 M107 M127 M521 M607 M1279 M2203 M2281 M3217 M4253 M4423 M9689 M9941 M11213
[edit] HicEst
s = 0
DO exponent = 2, 31
IF(exponent > 2) s = 4
n = 2^exponent - 1
DO i = 1, exponent-2
s = MOD(s*s - 2, n)
ENDDO
IF(s == 0) WRITE(Messagebox) 'M', exponent, ' is prime;', n
ENDDO
END
[edit] J
See Primality Tests essay on the J wiki.
[edit] Java
We use arbitrary-precision integers in order to be able to test any arbitrary prime.
import java.math.BigInteger;
public class Mersenne
{
public static boolean isPrime(int p) {
if (p == 2)
return true;
else if (p <= 1 || p % 2 == 0)
return false;
else {
int to = (int)Math.sqrt(p);
for (int i = 3; i <= to; i += 2)
if (p % i == 0)
return false;
return true;
}
}
public static boolean isMersennePrime(int p) {
if (p == 2)
return true;
else {
BigInteger m_p = BigInteger.ONE.shiftLeft(p).subtract(BigInteger.ONE);
BigInteger s = BigInteger.valueOf(4);
for (int i = 3; i <= p; i++)
s = s.multiply(s).subtract(BigInteger.valueOf(2)).mod(m_p);
return s.equals(BigInteger.ZERO);
}
}
// an arbitrary upper bound can be given as an argument
public static void main(String[] args) {
int upb;
if (args.length == 0)
upb = 500;
else
upb = Integer.parseInt(args[0]);
System.out.println(" Finding Mersenne primes in M[2.." + upb + "]: ");
for (int p = 3; p <= upb; p += 2)
if (isPrime(p) && isMersennePrime(p))
System.out.print(" M" + p);
System.out.println();
}
}
Output (after about eight hours):
Finding Mersenne primes in M[2..2147483647]: M2 M3 M5 M7 M13 M17 M19 M31 M61 M89 M107 M127 M521 M607 M1279 M2203 M2281 M3217 M4253 M4423 M9689 M9941 M11213
[edit] Mathematica
This version is very speedy and is bounded.
Select[Table[M = 2^p - 1;
For[i = 1; s = 4, i <= p - 2, i++, s = Mod[s^2 - 2, M]];
If[s == 0, "M" <> ToString@p, p], {p,
Prime /@ Range[300]}], StringQ]
=> {M3, M5, M7, M13, M17, M19, M31, M61, M89, M107, M127, M521, M607, M1279}
This version is unbounded (and timed):
t = SessionTime[];
For[p = 2, True, p = NextPrime[p], M = 2^p - 1;
For[i = 1; s = 4, i <= p - 2, i++, s = Mod[s^2 - 2, M]];
If[s == 0, Print["M" <> ToString@p]]]
(SessionTime[] - t) {Seconds, Minutes/60, Hours/3600, Days/86400}
I'll see what this gets.
[edit] MATLAB
MATLAB suffers from a lack of an arbitrary precision math (bignums) library. It also doesn't have great support for 64-bit integer arithmetic...or at least MATLAB 2007 doesn't. So, the best precision we have is doubles; therefore, this script can only find up to M19 and no greater.
function [mNumber,mersennesPrime] = mersennePrimes()
function isPrime = lucasLehmerTest(thePrime)
llResidue = 4;
mersennesPrime = (2^thePrime)-1;
for i = ( 1:thePrime-2 )
llResidue = mod( ((llResidue^2) - 2),mersennesPrime );
end
isPrime = (llResidue == 0);
end
%Because IEEE764 Double is the highest precision number we can
%represent in MATLAB, the highest Mersenne Number we can test is 2^52.
%In addition, because we have this cap, we can only test up to the
%number 30 for Mersenne Primeness. When we input 31 into the
%Lucas-Lehmer test, during the computation of the residue, the
%algorithm multiplies two numbers together the result of which is
%greater than 2^53. Because we require every digit to be significant,
%this leads to an error. The Lucas-Lehmer test should say that M31 is a
%Mersenne Prime, but because of the rounding error in calculating the
%residues caused by floating-point arithmetic, it does not. So M30 is
%the largest number we test.
mNumber = (3:30);
[isPrime] = arrayfun(@lucasLehmerTest,mNumber);
mNumber = [2 mNumber(isPrime)];
mersennesPrime = (2.^mNumber) - 1;
end
Ouput:
[mNumber,mersennesPrime] = mersennePrimes
mNumber =
2 3 5 7 13 17 19
mersennesPrime =
3 7 31 127 8191 131071 524287
[edit] Modula-3
Modula-3 uses L as the literal for LONGINT.
MODULE LucasLehmer EXPORTS Main;
IMPORT IO, Fmt, Long;
PROCEDURE Mersenne(p: CARDINAL): BOOLEAN =
VAR
s := 4L;
m := Long.Shift(1L, p) - 1L; (* 2^p - 1 *)
BEGIN
IF p = 2 THEN
RETURN TRUE;
ELSE
FOR i := 3 TO p DO
s := (s * s - 2L) MOD m;
END;
RETURN s = 0L;
END;
END Mersenne;
BEGIN
FOR i := 2 TO 63 DO
IF Mersenne(i) THEN
IO.Put("M" & Fmt.Int(i) & " ");
END;
END;
IO.Put("\n");
END LucasLehmer.
Output:
M2 M3 M5 M7 M13 M17 M19 M31
[edit] Oz
Oz's multiple precision number system use GMP core.
%% compile : ozc -x <file.oz>
functor
import
Application
System
define
fun {Arg Idx Default}
Cmd = {Application.getArgs plain}
Len = {Length Cmd}
in
if Len < Idx then
Default
else
{StringToInt {Nth Cmd Idx}}
end
end
fun {LLtest N}
Mp = {Pow 2 N} - 1
fun {S K} X T
in
if K == 1 then 4
else
T = {S K-1}
X = T * T - 2
X mod Mp
end
end
in
if N == 2 then
true
else
{S N-1} == 0
end
end
proc {FindLL X}
fun {Sieve Ls}
case Ls of nil then nil
[] X|Xs then
fun {DIV M} M mod X \= 0 end
in
X|{Sieve {Filter Xs DIV}}
end
end
in
if {IsList X} then
case X of nil then skip
[] M|Ms then
{System.printInfo "M"#M#" "}
{FindLL Ms}
end
else
{FindLL {Filter {Sieve 2|{List.number 3 X 2}} LLtest}}
end
end
Num = {Arg 1 607}
{FindLL Num}
{Application.exit 0}
end
[edit] Perl
Perl's Math::BigInt core module is a class that implements arbitrary-precision integers.
Here we use the bigint pragma to transparently have number constants and operations be bigints:
sub is_prime {
my $p = shift;
if ($p == 2) {
return 1;
} elsif ($p <= 1 || $p % 2 == 0) {
return 0;
} else {
my $limit = sqrt($p);
for (my $i = 3; $i <= $limit; $i += 2) {
return 0 if $p % $i == 0;
}
return 1;
}
}
sub is_mersenne_prime {
use bigint;
my $p = shift;
if ($p == 2) {
return 1;
} else {
my $m_p = 2 ** $p - 1;
my $s = 4;
foreach my $i (3 .. $p) {
$s = ($s ** 2 - 2) % $m_p;
}
return $s == 0;
}
}
my $precision = 20000; # maximum requested number of decimal places of 2 ** MP-1 #
my $long_bits_width = $precision / log(2) * log(10);
my $upb_prime = int(($long_bits_width - 1)/2); # no unsigned #
my $upb_count = 45; # find 45 mprimes if int was given enough bits #
print " Finding Mersenne primes in M[2..$upb_prime]:\n";
my $count = 0;
foreach my $p (2 .. $upb_prime) {
if (is_prime($p) && is_mersenne_prime($p)) {
print "M$p\n";
$count++;
}
last if $count >= $upb_count;
}
[edit] Perl 6
Translation of: Perl 5
Works with: Rakudo Star version 2010.08
Precision limited to 18 because rakudo does not yet implement arbitrary precision Int as specced.
multi is_prime(Int $p where ($p <= 1)) { False }
multi is_prime(Int $p) { $p %% none(2,(3,5...sqrt($p))) }
multi is_mersenne_prime(2) { True }
multi is_mersenne_prime(Int $p) {
my $m_p = 2 ** $p - 1;
my $s = 4;
$s = ($s ** 2 - 2) % $m_p for 3 .. $p;
$s == 0;
}
my $precision = 18; # maximum requested number of decimal places of 2 ** MP-1
my $long_bits_width = $precision / log(2) * log(10);
my $max_prime = floor(($long_bits_width - 1)/2);
my $max_count = 45;
say " Finding Mersenne primes in M[2..$max_prime]:";
my $count = 0;
for 2 .. $max_prime -> $p {
if is_prime($p) && is_mersenne_prime($p) {
say "M$p";
last if ++$count >= $max_count;
}
}
[edit] PicoLisp
(de prime? (N)
(or
(= N 2)
(and
(> N 1)
(bit? 1 N)
(for (D 3 T (+ D 2))
(T (> D (sqrt N)) T)
(T (=0 (% N D)) NIL) ) ) ) )
(de mersenne? (P)
(or
(= P 2)
(let (MP (dec (>> (- P) 1)) S 4)
(do (- P 2)
(setq S (% (- (* S S) 2) MP)) )
(=0 S) ) ) )
Output:
: (for N 10000 (and (prime? N) (mersenne? N) (println N)) ) 2 3 5 7 13 17 19 31 61 89 107 127 521 607 1279 2203 2281 3217 4253 4423 9689 9941
[edit] Pop11
Checking large numbers takes a lot of time so we limit p to be smaller than 1000.
define Lucas_Lehmer_Test(p);
lvars mp = 2**p - 1, sn = 4, i;
for i from 2 to p - 1 do
(sn*sn - 2) rem mp -> sn;
endfor;
sn = 0;
enddefine;
lvars p = 3;
printf('M2', '%p\n');
while p < 1000 do
if Lucas_Lehmer_Test(p) then
printf('M', '%p');
printf(p, '%p\n');
endif;
p + 2 -> p;
endwhile;
The output (obtained in few seconds) is:
M2
M3
M5
M7
M13
M17
M19
M31
M61
M89
M107
M127
M521
M607
[edit] PureBasic
PureBasic has no large integer support. Calculations are limited to the range of a signed quad integer type.
Procedure Lucas_Lehmer_Test(p)
Protected mp.q = (1 << p) - 1, sn.q = 4, i
For i = 3 To p
sn = (sn * sn - 2) % mp
Next
If sn = 0
ProcedureReturn #True
EndIf
ProcedureReturn #False
EndProcedure
#upperBound = SizeOf(Quad) * 8 - 1 ;equivalent to significant bits in a signed quad integer
If OpenConsole()
Define p = 3
PrintN("M2")
While p <= #upperBound
If Lucas_Lehmer_Test(p)
PrintN("M" + Str(p))
EndIf
p + 2
Wend
Print(#CRLF$ + #CRLF$ + "Press ENTER to exit"): Input()
CloseConsole()
EndIf
Sample output:
M2 M3 M5 M7 M13 M17 M19 M31
[edit] Python
from sys import stdout
from math import sqrt, log
def is_prime ( p ):
if p == 2: return True # Lucas-Lehmer test only works on odd primes
elif p <= 1 or p % 2 == 0: return False
else:
for i in range(3, int(sqrt(p))+1, 2 ):
if p % i == 0: return False
return True
def is_mersenne_prime ( p ):
if p == 2:
return True
else:
m_p = ( 1 << p ) - 1
s = 4
for i in range(3, p+1):
s = (s ** 2 - 2) % m_p
return s == 0
precision = 20000 # maximum requested number of decimal places of 2 ** MP-1 #
long_bits_width = precision / log(2) * log(10)
upb_prime = int( long_bits_width - 1 ) / 2 # no unsigned #
upb_count = 45 # find 45 mprimes if int was given enough bits #
print (" Finding Mersenne primes in M[2..%d]:"%upb_prime)
count=0
for p in range(2, upb_prime+1):
if is_prime(p) and is_mersenne_prime(p):
print("M%d"%p),
stdout.flush()
count += 1
if count >= upb_count: break
Output:
Finding Mersenne primes in M[2..33218]: M2 M3 M5 M7 M13 M17 M19 M31 M61 M89 M107 M127 M521 M607 M1279 M2203 M2281 M3217 M4253 M4423 M9689 M9941 M11213 M19937 M21701 M23209
[edit] Ruby
def is_prime ( p )
if p == 2
return true
elsif p <= 1 || p % 2 == 0
return false
else
(3 .. Math.sqrt(p)).step(2) do |i|
if p % i == 0
return false
end
end
return true
end
end
def is_mersenne_prime ( p )
if p == 2
return true
else
m_p = ( 1 << p ) - 1
s = 4
(p-2).times do
s = (s ** 2 - 2) % m_p
end
return s == 0
end
end
precision = 20000 # maximum requested number of decimal places of 2 ** MP-1 #
long_bits_width = precision / Math.log(2) * Math.log(10)
upb_prime = (long_bits_width - 1).to_i / 2 # no unsigned #
upb_count = 45 # find 45 mprimes if int was given enough bits #
puts " Finding Mersenne primes in M[2..%d]:"%upb_prime
count = 0
for p in 2..upb_prime
if is_prime(p) && is_mersenne_prime(p)
print "M%d "%p
count += 1
end
if count >= upb_count
break
end
end
puts
Output:
Finding Mersenne primes in M[2..33218]: M2 M3 M5 M7 M13 M17 M19 M31 M61 M89 M107 M127 M521 M607 M1279 M2203 M2281 M3217 M4253 M4423 M9689 M9941 M11213 M19937 M21701 M23209
[edit] Scheme
;;;The heart of the algorithm
(define (S n)
(let ((m (- (expt 2 n) 1)))
(let loop ((c (- n 2)) (a 4))
(if (zero? c)
a
(loop (- c 1) (remainder (- (* a a) 2) m))))))
(define (mersenne-prime? n)
(if (= n 2)
#t
(zero? (S n))))
;;;Trivial unoptimized implementation for the base primes
(define (next-prime x)
(if (prime? (+ x 1))
(+ x 1)
(next-prime (+ x 1))))
(define (prime? x)
(let loop ((c 2))
(cond ((>= c x) #t)
((zero? (remainder x c)) #f)
(else (loop (+ c 1))))))
;;Main loop
(let loop ((i 45) (p 2))
(if (not (zero? i))
(if (mersenne-prime? p)
(begin
(display "M") (display p) (display " ")
(loop (- i 1) (next-prime p)))
(loop i (next-prime p)))))
M2 M3 M5 M7 M13...
[edit] Tcl
Modeled after the Pop11 solution.
proc main argv {
set n 0
set t [clock seconds]
show_mersenne 2 [incr n] t
for {set p 3} {$p <= [lindex $argv 0]} {incr p 2} {
if {![prime $p]} continue
if {[LucasLehmer $p]} {
show_mersenne $p [incr n] t
}
}
}
proc show_mersenne {p n timevar} {
upvar 1 $timevar time
set now [clock seconds]
puts [format "%2d: %5ds M%s" $n [expr {$now - $time}] $p]
set time $now
}
proc prime i {
if {$i in {2 3}} {return 1}
prime0 $i [expr {int(sqrt($i))}]
}
proc prime0 {i div} {
expr {!($i % $div)? 0: $div <= 2? 1: [prime0 $i [incr div -1]]}
}
proc LucasLehmer p {
set mp [expr {2**$p-1}]
set s 4
for {set i 2} {$i < $p} {incr i} {
set s [expr {($s**2 - 2) % $mp}]
}
expr {$s == 0}
}
main 33218
Sample output. The program was still running, but as the next Mersenne prime is 19937 there will be a long wait until the program finds it.
1: 0s M2 2: 0s M3 3: 0s M5 4: 0s M7 5: 0s M13 6: 0s M17 7: 0s M19 8: 0s M31 9: 0s M61 10: 0s M89 11: 0s M107 12: 0s M127 13: 1s M521 14: 0s M607 15: 4s M1279 16: 21s M2203 17: 4s M2281 18: 69s M3217 19: 180s M4253 20: 39s M4423 21: 5543s M9689 22: 655s M9941 23: 3546s M11213
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