Data commit

Task/Attractive-numbers/C-sharp/attractive-numbers.cs

@@ -0,0 +1,55 @@
+using System;
+
+namespace AttractiveNumbers {
+    class Program {
+        const int MAX = 120;
+
+        static bool IsPrime(int n) {
+            if (n < 2) return false;
+            if (n % 2 == 0) return n == 2;
+            if (n % 3 == 0) return n == 3;
+            int d = 5;
+            while (d * d <= n) {
+                if (n % d == 0) return false;
+                d += 2;
+                if (n % d == 0) return false;
+                d += 4;
+            }
+            return true;
+        }
+
+        static int PrimeFactorCount(int n) {
+            if (n == 1) return 0;
+            if (IsPrime(n)) return 1;
+            int count = 0;
+            int f = 2;
+            while (true) {
+                if (n % f == 0) {
+                    count++;
+                    n /= f;
+                    if (n == 1) return count;
+                    if (IsPrime(n)) f = n;
+                } else if (f >= 3) {
+                    f += 2;
+                } else {
+                    f = 3;
+                }
+            }
+        }
+
+        static void Main(string[] args) {
+            Console.WriteLine("The attractive numbers up to and including {0} are:", MAX);
+            int i = 1;
+            int count = 0;
+            while (i <= MAX) {
+                int n = PrimeFactorCount(i);
+                if (IsPrime(n)) {
+                    Console.Write("{0,4}", i);
+                    if (++count % 20 == 0) Console.WriteLine();
+                }
+                ++i;
+            }
+            Console.WriteLine();
+        }
+    }
+}