Blum integer: Difference between revisions

=={{header|C}}==

{{trans|Wren}}

<syntaxhighlight lang="c">#include <stdio.h>

#include <stdbool.h>

#include <locale.h>

bool isPrime(int n) {

if (n < 2) return false;

if (n%2 == 0) return n == 2;

if (n%3 == 0) return n == 3;

int d = 5;

while (d*d <= n) {

if (n%d == 0) return false;

d += 2;

if (n%d == 0) return false;

d += 4;

}

return true;

}

void primeFactors(int n, int *factors, int *length) {

if (n < 2) return;

int count = 0;

int inc[8] = {4, 2, 4, 2, 4, 6, 2, 6};

while (!(n%2)) {

factors[count++] = 2;

n /= 2;

}

while (!(n%3)) {

factors[count++] = 3;

n /= 3;

}

while (!(n%5)) {

factors[count++] = 5;

n /= 5;

}

for (int k = 7, i = 0; k*k <= n; ) {

if (!(n%k)) {

factors[count++] = k;

n /= k;

} else {

k += inc[i];

i = (i + 1) % 8;

}

}

if (n > 1) {

factors[count++] = n;

}

*length = count;

}

int main() {

int i = 1, j, bc = 0, length = 0;

int f[20], blum[50], counts[4] = {0}, digits[4] = {1, 3, 5, 7};

setlocale(LC_NUMERIC, "");

while (true) {

primeFactors(i, f, &length);

if (length == 2 && f[0] != f[1] && f[0] % 4 == 3 && f[1] % 4 == 3) {

if (bc < 50) blum[bc] = i;

++counts[i % 10 / 3];

++bc;

if (bc == 50) {

printf("First 50 Blum integers:\n");

for (j = 0; j < 50; ++j) {

printf("%3d ", blum[j]);

if (!((j+1) % 10)) printf("\n");

}

printf("\n");

} else if (bc == 26828 || !(bc % 100000)) {

printf("The %'7dth Blum integer is: %'9d\n", bc, i);

if (bc == 400000) {

printf("\n%% distribution of the first 400,000 Blum integers:\n");

for (j = 0; j < 4; ++j) {

printf(" %6.3f%% end in %d\n", counts[j]/4000.0, digits[j]);

}

break;

}

}

}

i = (i % 5 == 3) ? i + 4 : i + 2;

}

return 0;

}</syntaxhighlight>

{{out}}

<pre>

Same as Wren example.

</pre>