Initial data commit

Task/Attractive-numbers/Java/attractive-numbers.java

@@ -0,0 +1,45 @@
+public class Attractive {
+
+    static boolean is_prime(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 count_prime_factors(int n) {
+        if (n == 1) return 0;
+        if (is_prime(n)) return 1;
+        int count = 0, f = 2;
+        while (true) {
+            if (n % f == 0) {
+                count++;
+                n /= f;
+                if (n == 1) return count;
+                if (is_prime(n)) f = n;
+            }
+            else if (f >= 3) f += 2;
+            else f = 3;
+        }
+    }
+
+    public static void main(String[] args) {
+        final int max = 120;
+        System.out.printf("The attractive numbers up to and including %d are:\n", max);
+        for (int i = 1, count = 0; i <= max; ++i) {
+            int n = count_prime_factors(i);
+            if (is_prime(n)) {
+                System.out.printf("%4d", i);
+                if (++count % 20 == 0) System.out.println();
+            }
+        }
+        System.out.println();
+    }
+}