2016 Update

Task/Amicable-pairs/JavaScript/amicable-pairs-3.js

@@ -0,0 +1,46 @@
+(max => {
+
+    // amicablePairsUpTo :: Int -> [(Int, Int)]
+    let amicablePairsUpTo = max =>
+        range(1, max)
+        .map(x => properDivisors(x)
+            .reduce((a, b) => a + b, 0))
+        .reduce((a, m, i, lst) => {
+            let n = i + 1;
+
+            return (m > n) && lst[m - 1] === n ?
+                a.concat([[n, m]]) : a;
+        }, []),
+
+
+        // properDivisors :: Int -> [Int]
+        properDivisors = n => {
+            if (n < 2) return [];
+            else {
+                let rRoot = Math.sqrt(n),
+                    intRoot = Math.floor(rRoot),
+                    blnPerfectSquare = rRoot === intRoot,
+
+                    lows = range(1, intRoot)
+                    .filter(x => (n % x) === 0);
+
+                return lows.concat(lows.slice(1)
+                    .map(x => n / x)
+                    .reverse()
+                    .slice(blnPerfectSquare | 0));
+            }
+        },
+
+        // Int -> Int -> Maybe Int -> [Int]
+        range = (m, n, step) => {
+            let d = (step || 1) * (n >= m ? 1 : -1);
+
+            return Array.from({
+                length: Math.floor((n - m) / d) + 1
+            }, (_, i) => m + (i * d));
+        }
+
+
+    return amicablePairsUpTo(max);
+
+})(20000);

Task/Amicable-pairs/JavaScript/amicable-pairs-4.js

@@ -0,0 +1,2 @@
+[[220, 284], [1184, 1210], [2620, 2924], [5020, 5564],
+[6232, 6368], [10744, 10856], [12285, 14595], [17296, 18416]]