Data commit

Task/Chowla-numbers/C/chowla-numbers.c

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