Initial data commit

Task/Chowla-numbers/Java/chowla-numbers.java

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+public class Chowla {
+
+    public static void main(String[] args) {
+        int[] chowlaNumbers = findChowlaNumbers(37);
+        for (int i = 0; i < chowlaNumbers.length; i++) {
+            System.out.printf("chowla(%d) = %d%n", (i+1), chowlaNumbers[i]);
+        }
+        System.out.println();
+
+        int[][] primes = countPrimes(100, 10_000_000);
+        for (int i = 0; i < primes.length; i++) {
+            System.out.printf(Locale.US, "There is %,d primes up to %,d%n", primes[i][1], primes[i][0]);
+        }
+        System.out.println();
+
+        int[] perfectNumbers = findPerfectNumbers(35_000_000);
+        for (int i = 0; i < perfectNumbers.length; i++) {
+            System.out.printf("%d is a perfect number%n", perfectNumbers[i]);
+        }
+        System.out.printf(Locale.US, "There are %d perfect numbers < %,d%n", perfectNumbers.length, 35_000_000);
+    }
+
+    public static int chowla(int n) {
+        if (n < 0) throw new IllegalArgumentException("n is not positive");
+        int sum = 0;
+        for (int i = 2, j; i * i <= n; i++)
+            if (n % i == 0) sum += i + (i == (j = n / i) ? 0 : j);
+        return sum;
+    }
+
+    protected static int[][] countPrimes(int power, int limit) {
+        int count = 0;
+        int[][] num = new int[countMultiplicity(limit, power)][2];
+        for (int n = 2, i=0;  n <= limit; n++) {
+            if (chowla(n) == 0) count++;
+            if (n % power == 0) {
+                num[i][0] = power;
+                num[i][1] = count;
+                i++;
+                power *= 10;
+            }
+        }
+        return num;
+    }
+
+    protected static int countMultiplicity(int limit, int start) {
+        int count = 0;
+        int cur = limit;
+        while(cur >= start) {
+            count++;
+            cur = cur/10;
+        }
+        return count;
+    }
+
+    protected static int[] findChowlaNumbers(int limit) {
+        int[] num = new int[limit];
+        for (int i = 0; i < limit; i++) {
+            num[i] = chowla(i+1);
+        }
+        return num;
+    }
+
+    protected static int[] findPerfectNumbers(int limit) {
+        int count = 0;
+        int[] num = new int[count];
+
+        int k = 2, kk = 3, p;
+        while ((p = k * kk) < limit) {
+            if (chowla(p) == p - 1) {
+                num = increaseArr(num);
+                num[count++] = p;
+            }
+            k = kk + 1;
+            kk += k;
+        }
+        return num;
+    }
+
+    private static int[] increaseArr(int[] arr) {
+        int[] tmp = new int[arr.length + 1];
+        System.arraycopy(arr, 0, tmp, 0, arr.length);
+        return tmp;
+    }
+}