Data commit

Task/Chernicks-Carmichael-numbers/C/chernicks-carmichael-numbers.c

@@ -0,0 +1,51 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <gmp.h>
+
+typedef unsigned long long int u64;
+
+#define TRUE 1
+#define FALSE 0
+
+int primality_pretest(u64 k) {
+    if (!(k %  3) || !(k %  5) || !(k %  7) || !(k % 11) || !(k % 13) || !(k % 17) || !(k % 19) || !(k % 23)) return (k <= 23);
+    return TRUE;
+}
+
+int probprime(u64 k, mpz_t n) {
+    mpz_set_ui(n, k);
+    return mpz_probab_prime_p(n, 0);
+}
+
+int is_chernick(int n, u64 m, mpz_t z) {
+    u64 t = 9 * m;
+    if (primality_pretest(6 * m + 1) == FALSE) return FALSE;
+    if (primality_pretest(12 * m + 1) == FALSE) return FALSE;
+    for (int i = 1; i <= n - 2; i++) if (primality_pretest((t << i) + 1) == FALSE) return FALSE;
+    if (probprime(6 * m + 1, z) == FALSE) return FALSE;
+    if (probprime(12 * m + 1, z) == FALSE) return FALSE;
+    for (int i = 1; i <= n - 2; i++) if (probprime((t << i) + 1, z) == FALSE) return FALSE;
+    return TRUE;
+}
+
+int main(int argc, char const *argv[]) {
+    mpz_t z;
+    mpz_inits(z, NULL);
+
+    for (int n = 3; n <= 10; n ++) {
+        u64 multiplier = (n > 4) ? (1 << (n - 4)) : 1;
+
+        if (n > 5) multiplier *= 5;
+
+        for (u64 k = 1; ; k++) {
+            u64 m = k * multiplier;
+
+            if (is_chernick(n, m, z) == TRUE) {
+                printf("a(%d) has m = %llu\n", n, m);
+                break;
+            }
+        }
+    }
+
+    return 0;
+}