Data commit

Task/Chowla-numbers/Go/chowla-numbers.go

@@ -0,0 +1,80 @@
+package main
+
+import "fmt"
+
+func chowla(n int) int {
+    if n < 1 {
+        panic("argument must be a positive integer")
+    }
+    sum := 0
+    for i := 2; i*i <= n; i++ {
+        if n%i == 0 {
+            j := n / i
+            if i == j {
+                sum += i
+            } else {
+                sum += i + j
+            }
+        }
+    }
+    return sum
+}
+
+func sieve(limit int) []bool {
+    // True denotes composite, false denotes prime.
+    // Only interested in odd numbers >= 3
+    c := make([]bool, limit)
+    for i := 3; i*3 < limit; i += 2 {
+        if !c[i] && chowla(i) == 0 {
+            for j := 3 * i; j < limit; j += 2 * i {
+                c[j] = true
+            }
+        }
+    }
+    return c
+}
+
+func commatize(n int) string {
+    s := fmt.Sprintf("%d", n)
+    le := len(s)
+    for i := le - 3; i >= 1; i -= 3 {
+        s = s[0:i] + "," + s[i:]
+    }
+    return s
+}
+
+func main() {
+    for i := 1; i <= 37; i++ {
+        fmt.Printf("chowla(%2d) = %d\n", i, chowla(i))
+    }
+    fmt.Println()
+
+    count := 1
+    limit := int(1e7)
+    c := sieve(limit)
+    power := 100
+    for i := 3; i < limit; i += 2 {
+        if !c[i] {
+            count++
+        }
+        if i == power-1 {
+            fmt.Printf("Count of primes up to %-10s = %s\n", commatize(power), commatize(count))
+            power *= 10
+        }
+    }
+
+    fmt.Println()
+    count = 0
+    limit = 35000000
+    for i := uint(2); ; i++ {
+        p := 1 << (i - 1) * (1<<i - 1) // perfect numbers must be of this form
+        if p > limit {
+            break
+        }
+        if chowla(p) == p-1 {
+            fmt.Printf("%s is a perfect number\n", commatize(p))
+            count++
+        }
+    }
+    fmt.Println("There are", count, "perfect numbers <= 35,000,000")
+}