Erdös-Selfridge categorization of primes: Difference between revisions
Erdös-Selfridge categorization of primes (view source)
Revision as of 16:43, 16 May 2023
, 1 year agoCreated Nim solution.
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10 1065601 15472321 28
11 8524807 8524807 1</pre>
=={{header|Nim}}==
{{trans|Wren}}
Translation of Wren program with some modifications. As we don’t use a library to find the prime factors, we defined our own function to return the list without duplicates.
The program runs in about 2.5 seconds.
<syntaxhighlight lang="Nim">import std/[bitops, math, sequtils, strformat, strutils, tables]
type Sieve = object
data: seq[byte]
func `[]`(sieve: Sieve; idx: Positive): bool =
## Return value of element at index "idx".
let idx = idx shr 1
let iByte = idx shr 3
let iBit = idx and 7
result = sieve.data[iByte].testBit(iBit)
func `[]=`(sieve: var Sieve; idx: Positive; val: bool) =
## Set value of element at index "idx".
let idx = idx shr 1
let iByte = idx shr 3
let iBit = idx and 7
if val: sieve.data[iByte].setBit(iBit)
else: sieve.data[iByte].clearBit(iBit)
func newSieve(lim: Positive): Sieve =
## Create a sieve with given maximal index.
result.data = newSeq[byte]((lim + 16) shr 4)
func initPrimes(lim: Positive): seq[Natural] =
## Initialize the list of primes from 2 to "lim".
var composite = newSieve(lim)
composite[1] = true
for n in countup(3, sqrt(lim.toFloat).int, 2):
if not composite[n]:
for k in countup(n * n, lim, 2 * n):
composite[k] = true
result.add 2
for n in countup(3, lim, 2):
if not composite[n]:
result.add n
const Limit = int(ln(1e6) * 1e6 * 1.2)
let primes = initPrimes(Limit)
func primeFactors(n: Positive): seq[Positive] =
## Return the list of prime factors of "n".
## Duplicate primes are excluded.
var n = n
var last = 0
while (n and 1) == 0:
if last != 2:
result.add 2
last = 2
n = n shr 1
var d = 3
while d * d <= n:
while n mod d == 0:
if last != d:
result.add d
last = d
n = n div d
inc d, 2
if n > 1: result.add n
type Category = 1..12
var prevCats: Table[int, int]
proc cat(p: Natural): Category =
## Recursive procedure to compute the catagory of "p".
if p in prevCats: return prevCats[p]
let pf = primeFactors(p + 1)
if pf.allIt(it == 2 or it == 3):
return 1
for c in 2..11:
if pf.allIt(cat(it) < c):
prevCats[p] = c
return c
result = 12
var es: array[Category, seq[Positive]]
echo "First 200 primes:\n"
for p in primes[0..199]:
es[p.cat].add p
for c in 1..6:
if es[c].len > 0:
echo &"Category {c}:"
echo es[c].join(" ")
echo()
echo "First million primes:\n"
for p in primes[200..999_999]:
es[p.cat].add p
for c in 1..12:
let e = es[c]
if e.len > 0:
echo &"Category {c:>2}: first = {e[0]:>7} last = {e[^1]:>8} count = {e.len:>6}"
</syntaxhighlight>
{{out}}
<pre>First 200 primes:
Category 1:
2 3 5 7 11 17 23 31 47 53 71 107 127 191 383 431 647 863 971 1151
Category 2:
13 19 29 41 43 59 61 67 79 83 89 97 101 109 131 137 139 149 167 179 197 199 211 223 229 239 241 251 263 269 271 281 283 293 307 317 349 359 367 373 419 433 439 449 461 479 499 503 509 557 563 577 587 593 599 619 641 643 659 709 719 743 751 761 769 809 827 839 881 919 929 953 967 991 1019 1033 1049 1069 1087 1103 1187 1223
Category 3:
37 103 113 151 157 163 173 181 193 227 233 257 277 311 331 337 347 353 379 389 397 401 409 421 457 463 467 487 491 521 523 541 547 569 571 601 607 613 631 653 683 701 727 733 773 787 797 811 821 829 853 857 859 877 883 911 937 947 983 997 1009 1013 1031 1039 1051 1061 1063 1091 1097 1117 1123 1153 1163 1171 1181 1193 1217
Category 4:
73 313 443 617 661 673 677 691 739 757 823 887 907 941 977 1093 1109 1129 1201 1213
Category 5:
1021
First million primes:
Category 1: first = 2 last = 10616831 count = 46
Category 2: first = 13 last = 15482669 count = 10497
Category 3: first = 37 last = 15485863 count = 201987
Category 4: first = 73 last = 15485849 count = 413891
Category 5: first = 1021 last = 15485837 count = 263109
Category 6: first = 2917 last = 15485857 count = 87560
Category 7: first = 15013 last = 15484631 count = 19389
Category 8: first = 49681 last = 15485621 count = 3129
Category 9: first = 532801 last = 15472811 count = 363
Category 10: first = 1065601 last = 15472321 count = 28
Category 11: first = 8524807 last = 8524807 count = 1
</pre>
=={{header|Perl}}==
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