Data commit

Task/Perfect-totient-numbers/Java/perfect-totient-numbers.java

@@ -0,0 +1,45 @@
+import java.util.ArrayList;
+import java.util.List;
+
+public class PerfectTotientNumbers {
+
+    public static void main(String[] args) {
+        computePhi();
+        int n = 20;
+        System.out.printf("The first %d perfect totient numbers:%n%s%n", n, perfectTotient(n));
+    }
+
+    private static final List<Integer> perfectTotient(int n) {
+        int test = 2;
+        List<Integer> results = new ArrayList<Integer>();
+        for ( int i = 0 ; i < n ; test++ ) {
+            int phiLoop = test;
+            int sum = 0;
+            do {
+                phiLoop = phi[phiLoop];
+                sum += phiLoop;
+            } while ( phiLoop > 1);
+            if ( sum == test ) {
+                i++;
+                results.add(test);
+            }
+        }
+        return results;
+    }
+
+    private static final int max = 100000;
+    private static final int[] phi = new int[max+1];
+
+    private static final void computePhi() {
+        for ( int i = 1 ; i <= max ; i++ ) {
+            phi[i] = i;
+        }
+        for ( int i = 2 ; i <= max ; i++ ) {
+            if (phi[i] < i) continue;
+            for ( int j = i ; j <= max ; j += i ) {
+                phi[j] -= phi[j] / i;
+            }
+        }
+    }
+
+}