Chowla numbers: Difference between revisions

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 There are 5 perfect numbers <= 35,000,000
 </pre>
+=={{header|Groovy}}==
+{{trans|Kotlin}}
+<lang groovy>class Chowla {
+    static int chowla(int n) {
+        if (n < 1) throw new RuntimeException("argument must be a positive integer")
+        int sum = 0
+        int i = 2
+        while (i * i <= n) {
+            if (n % i == 0) {
+                int j = (int) (n / i)
+                sum += (i == j) ? i : i + j
+            }
+            i++
+        }
+        return sum
+    }
+    static boolean[] sieve(int limit) {
+        // True denotes composite, false denotes prime.
+        // Only interested in odd numbers >= 3
+        boolean[] c = new boolean[limit]
+        for (int i = 3; i < limit / 3; i += 2) {
+            if (!c[i] && chowla(i) == 0) {
+                for (int j = 3 * i; j < limit; j += 2 * i) {
+                    c[j] = true
+                }
+            }
+        }
+        return c
+    }
+    static void main(String[] args) {
+        for (int i = 1; i <= 37; i++) {
+            printf("chowla(%2d) = %d\n", i, chowla(i))
+        }
+        println()
+        int count = 1
+        int limit = 10_000_000
+        boolean[] c = sieve(limit)
+        int power = 100
+        for (int i = 3; i < limit; i += 2) {
+            if (!c[i]) {
+                count++
+            }
+            if (i == power - 1) {
+                printf("Count of primes up to %,10d = %,7d\n", power, count)
+                power *= 10
+            }
+        }
+        println()
+        count = 0
+        limit = 35_000_000
+        int i = 2
+        while (true) {
+            int p = (1 << (i - 1)) * ((1 << i) - 1) // perfect numbers must be of this form
+            if (p > limit) break
+            if (chowla(p) == p - 1) {
+                printf("%,d is a perfect number\n", p)
+                count++
+            }
+            i++
+        }
+        printf("There are %,d perfect numbers <= %,d\n", count, limit)
+    }
+}</lang>
+{{out}}
+<pre>chowla( 1) = 0
+chowla( 2) = 0
+chowla( 3) = 0
+chowla( 4) = 2
+chowla( 5) = 0
+chowla( 6) = 5
+chowla( 7) = 0
+chowla( 8) = 6
+chowla( 9) = 3
+chowla(10) = 7
+chowla(11) = 0
+chowla(12) = 15
+chowla(13) = 0
+chowla(14) = 9
+chowla(15) = 8
+chowla(16) = 14
+chowla(17) = 0
+chowla(18) = 20
+chowla(19) = 0
+chowla(20) = 21
+chowla(21) = 10
+chowla(22) = 13
+chowla(23) = 0
+chowla(24) = 35
+chowla(25) = 5
+chowla(26) = 15
+chowla(27) = 12
+chowla(28) = 27
+chowla(29) = 0
+chowla(30) = 41
+chowla(31) = 0
+chowla(32) = 30
+chowla(33) = 14
+chowla(34) = 19
+chowla(35) = 12
+chowla(36) = 54
+chowla(37) = 0
+Count of primes up to        100 =      25
+Count of primes up to      1,000 =     168
+Count of primes up to     10,000 =   1,229
+Count of primes up to    100,000 =   9,592
+Count of primes up to  1,000,000 =  78,498
+Count of primes up to 10,000,000 = 664,579
+is a perfect number
+is a perfect number
+is a perfect number
+,128 is a perfect number
+,550,336 is a perfect number
+There are 5 perfect numbers <= 35,000,000</pre>
 =={{header|J}}==