>>738 c
https://ideone.com/Dbl6mc
#include <stdlib.h>
#include <math.h>
#include <stdio.h>
void sieve_of_eratosthenes(int n, int **isprime, int **primes_beg, int **primes_end) {
int i, m, j, nbytes = (1 + n) * sizeof **isprime, *map = malloc(nbytes), *beg = malloc(nbytes), *end;
for (i = 2; i <= n; i++) map[i] = 1;
for (i = 2, m = sqrt(n); i <= m; i++)
if (map[i]) for (j = i * i; j <= n; j += i) map[j] = 0;
for (i = 2, end = beg; i <= n; i++) if (map[i]) *end++ = i;
*isprime = map, *primes_beg = beg, *primes_end = end;
}
int main() {
int n = 1234567, *isprime, *primes_beg, *primes_end;
sieve_of_eratosthenes(n, &isprime, &primes_beg, &primes_end);

int *a, *b, c, count = 0;
for (a = primes_beg; a < primes_end && *a <= n / 3; a++)
for (b = a; b < primes_end && *b <= (c = n - *a - *b); b++)
if (isprime[c]) count++;
printf("count = %d\n", count);
return 0;
}