Problem 46

46.c

@@ -0,0 +1,37 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+#include <stdbool.h>
+#include "primes.h"
+
+int main () {
+    long size = 10000;
+    long* primes;
+    bool* primesTable;
+    long numPrimes = listOfPrimes (size, &primes, &primesTable);
+    long n = 37;
+    while (n < size) {
+        if (!primesTable[n]) {
+            long p = 0;
+            bool decomposable = false;
+            while (n > primes[p]) {
+                long sq = (n - primes[p]) / 2;
+                long sqrtr = sqrt (sq);
+                if (sqrtr * sqrtr == sq) {
+                    // printf ("%lli = %lli + 2 x %lli²\n", n, primes[p], sqrtr);
+                    decomposable = true;
+                    n += 2;
+                    break;
+                }
+                else
+                    p++;
+            }
+            if (!decomposable) {
+                printf ("%lli cannot be written as such.\n", n);
+                break;
+            }
+        }
+        else
+            n += 2;
+    }
+}