32 lines
857 B
C
32 lines
857 B
C
#include <stdio.h>
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unsigned chowla(const unsigned n) {
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unsigned sum = 0;
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for (unsigned i = 2, j; i * i <= n; i ++) if (n % i == 0) sum += i + (i == (j = n / i) ? 0 : j);
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return sum;
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}
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int main(int argc, char const *argv[]) {
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unsigned a;
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for (unsigned n = 1; n < 38; n ++) printf("chowla(%u) = %u\n", n, chowla(n));
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unsigned n, count = 0, power = 100;
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for (n = 2; n < 10000001; n ++) {
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if (chowla(n) == 0) count ++;
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if (n % power == 0) printf("There is %u primes < %u\n", count, power), power *= 10;
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}
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count = 0;
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unsigned limit = 350000000;
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unsigned k = 2, kk = 3, p;
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for ( ; ; ) {
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if ((p = k * kk) > limit) break;
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if (chowla(p) == p - 1) {
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printf("%d is a perfect number\n", p);
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count ++;
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}
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k = kk + 1; kk += k;
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}
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printf("There are %u perfect numbers < %u\n", count, limit);
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return 0;
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}
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