Data commit

Task/Duffinian-numbers/Julia/duffinian-numbers.julia

@@ -0,0 +1,28 @@
+using Primes
+
+function σ(n)
+    f = [one(n)]
+    for (p,e) in factor(n)
+        f = reduce(vcat, [f*p^j for j in 1:e], init=f)
+    end
+    return sum(f)
+end
+
+isDuffinian(n) = !isprime(n) && gcd(n, σ(n)) == 1
+
+function testDuffinians()
+    println("First 50 Duffinian numbers:")
+    foreach(p -> print(rpad(p[2], 4), p[1] % 25 == 0 ? "\n" : ""),
+        enumerate(filter(isDuffinian, 2:217)))
+    n, found = 2, 0
+    println("\nFifteen Duffinian triplets:")
+    while found < 15
+        if isDuffinian(n) && isDuffinian(n + 1) && isDuffinian(n + 2)
+            println(lpad(n, 6), lpad(n +1, 6), lpad(n + 2, 6))
+            found += 1
+        end
+        n += 1
+    end
+end
+
+testDuffinians()