Add problem 46 solution

primes.h

@@ -0,0 +1,21 @@
+int is_prime(long num)
+{
+	int i = 5;
+	int w = 2;
+
+	if (num == 1)
+		return 0;
+	if (num == 2 || num == 3)
+		return 1;
+	if (!(num%2) || !(num%3))
+		return 0;
+
+	while ((i*i) <= num) {
+		if (!(num%i))
+			return 0;
+		i += w;
+		w = 6 - w;
+	}
+
+	return 1;
+}