Data update

Task/Magic-constant/C/magic-constant.c

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+/* Magic constant */
+#include<stdio.h>
+#include<math.h>
+
+/* returns the magic constant of a magic square of order n + 2 */
+long a(int n)
+{
+  long n2 = n + 2;
+  return (n2 * ((n2 * n2) + 1)) / 2;
+}
+
+/* returns the order of the magic square whose magic constant is at least x */
+long inv_a(double x)
+{
+  return (long)pow((2. * x), 1. / 3.) + 1;
+}
+
+int main()
+{
+  int n;
+  double e = 1.; /* final values can be greater than MAX_LONG */
+  printf("The first 20 magic constants are ");
+  for (n = 1; n <= 20; n++)
+    printf("%d ", a(n));
+  printf("\n");
+  printf("The 1,000th magic constant is %d\n", a(1000));
+  for (n = 1; n <= 20; n++)
+  {
+    e *= 10;
+    printf("10^%2d: %9d\n", n, inv_a(e));
+  }
+}