Data commit

Task/Duffinian-numbers/Go/duffinian-numbers.go

@@ -0,0 +1,52 @@
+package main
+
+import (
+    "fmt"
+    "math"
+    "rcu"
+)
+
+func isSquare(n int) bool {
+    s := int(math.Sqrt(float64(n)))
+    return s*s == n
+}
+
+func main() {
+    limit := 200000 // say
+    d := rcu.PrimeSieve(limit-1, true)
+    d[1] = false
+    for i := 2; i < limit; i++ {
+        if !d[i] {
+            continue
+        }
+        if i%2 == 0 && !isSquare(i) && !isSquare(i/2) {
+            d[i] = false
+            continue
+        }
+        sigmaSum := rcu.SumInts(rcu.Divisors(i))
+        if rcu.Gcd(sigmaSum, i) != 1 {
+            d[i] = false
+        }
+    }
+
+    var duff []int
+    for i := 1; i < len(d); i++ {
+        if d[i] {
+            duff = append(duff, i)
+        }
+    }
+    fmt.Println("First 50 Duffinian numbers:")
+    rcu.PrintTable(duff[0:50], 10, 3, false)
+
+    var triplets [][3]int
+    for i := 2; i < limit; i++ {
+        if d[i] && d[i-1] && d[i-2] {
+            triplets = append(triplets, [3]int{i - 2, i - 1, i})
+        }
+    }
+    fmt.Println("\nFirst 56 Duffinian triplets:")
+    for i := 0; i < 14; i++ {
+        s := fmt.Sprintf("%6v", triplets[i*4:i*4+4])
+        fmt.Println(s[1 : len(s)-1])
+    }
+}