Cousin primes: Difference between revisions
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There are 41 cousin prime pairs below 1000</pre> |
There are 41 cousin prime pairs below 1000</pre> |
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=={{header|C}}== |
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<lang c>#include <stdio.h> |
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#include <string.h> |
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#define LIMIT 1000 |
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void sieve(int max, char *s) { |
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int p, k; |
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memset(s, 0, max); |
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for (p=2; p*p<=max; p++) |
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if (!s[p]) |
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for (k=p*p; k<=max; k+=p) |
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s[k]=1; |
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} |
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int main(void) { |
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char primes[LIMIT+1]; |
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int p, count=0; |
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sieve(LIMIT, primes); |
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for (p=2; p<=LIMIT; p++) { |
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if (!primes[p] && !primes[p+4]) { |
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count++; |
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printf("%4d: %4d\n", p, p+4); |
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} |
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} |
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printf("There are %d cousin prime pairs below %d.\n", count, LIMIT); |
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return 0; |
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}</lang> |
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{{out}} |
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<pre style="height:14em;"> 3: 7 |
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7: 11 |
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13: 17 |
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19: 23 |
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37: 41 |
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43: 47 |
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67: 71 |
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79: 83 |
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97: 101 |
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103: 107 |
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109: 113 |
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127: 131 |
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163: 167 |
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193: 197 |
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223: 227 |
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229: 233 |
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277: 281 |
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307: 311 |
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313: 317 |
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349: 353 |
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379: 383 |
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397: 401 |
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439: 443 |
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457: 461 |
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463: 467 |
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487: 491 |
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499: 503 |
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613: 617 |
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643: 647 |
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673: 677 |
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739: 743 |
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757: 761 |
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769: 773 |
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823: 827 |
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853: 857 |
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859: 863 |
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877: 881 |
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883: 887 |
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907: 911 |
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937: 941 |
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967: 971 |
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There are 41 cousin prime pairs below 1000.</pre> |
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=={{header|Cowgol}}== |
=={{header|Cowgol}}== |