ソースコード void sieve_of_atkin() { int n; for (int z = 1; z <= 5; z += 4) { for (int y = z; y <= sqrtN; y += 6) { for (int x = 1; x <= sqrtN && (n = 4*x*x+y*y) <= N; ++x) isprime[n] = !isprime[n]; for (int x = y+1; x <= sqrtN && (n = 3*x*x-y*y) <= N; x += 2) isprime[n] = !isprime[n]; } } for (int z = 2; z <= 4; z += 2) { for (int y = z; y <= sqrtN; y += 6) { for (int x = 1; x <= sqrtN && (n = 3*x*x+y*