algorithm: aliquot sum (#60)

Author: SpiderMath

Maths/AliquotSum.ts

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+/**
+ * @function AliquotSum
+ * @description Returns the aliquot sum of the provided number
+ * @summary The aliquot sum of a number n is the sum of all the proper divisors
+ * of n apart from n itself.
+ * So, for example, the number 6 has three proper divisors, 1, 2, 3
+ * Hence its aliquot sum is 1 + 2 + 3 = 6
+ * For all prime numbers, the aliquot sum is 1, and for 1, the aliquot sum is 0
+ * @param {number} num The input number
+ * @return {number} The aliquot sum of the number
+ * @see [Wikipedia](https://en.wikipedia.org/wiki/Aliquot_sum)
+ * @example AliquotSum(18) = 21
+ * @example AliquotSum(15) = 9
+ */
+export const AliquotSum = (num: number): number => {
+  if (typeof num !== 'number') throw new TypeError('Input needs to be a number')
+  if (num < 0) throw new TypeError('Input cannot be negative')
+  if (!Number.isInteger(num)) throw new TypeError('Input cannot be a decimal')
+
+  let sum = 0
+
+  for (let i = 1; i <= num / 2; i++) {
+    if (num % i === 0) sum += i;
+  }
+
+  return sum
+}

Maths/test/AliquotSum.test.ts

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+import { AliquotSum } from "../AliquotSum";
+
+test.each([[15, 9], [18, 21], [28, 28], [100, 117], [169, 14], [1729, 511], [15625, 3906]])("Aliquot Sum of %i is %i", (num, expected) => {
+  expect(AliquotSum(num)).toBe(expected)
+})