feat: add abundant number algorithm

Maths/AbundantNumber.js

@@ -0,0 +1,27 @@
+/**
+ * @function isAbundantNumber
+ * @description An abundant number is a positive integer for which the
+ *   sum of its proper divisors is greater than the number itself.
+ *   For example, 12 is abundant because 1+2+3+4+6=16 > 12.
+ * @param {number} n - A positive integer
+ * @returns {boolean} - True if n is an abundant number, false otherwise
+ * @see https://en.wikipedia.org/wiki/Abundant_number
+ * @example isAbundantNumber(12) => true
+ * @example isAbundantNumber(18) => true
+ * @example isAbundantNumber(9) => false
+ */
+const isAbundantNumber = (n) => {
+  if (!Number.isInteger(n) || n < 1) {
+    throw new TypeError('Input must be a positive integer')
+  }
+  let sum = 1
+  for (let i = 2; i <= Math.sqrt(n); i++) {
+    if (n % i === 0) {
+      sum += i
+      if (i !== n / i) sum += n / i
+    }
+  }
+  return sum > n
+}
+
+export { isAbundantNumber }

Maths/test/AbundantNumber.test.js

@@ -0,0 +1,47 @@
+import { isAbundantNumber } from '../AbundantNumber.js'
+
+describe('isAbundantNumber', () => {
+  test('12 is an abundant number (1+2+3+4+6=16>12)', () => {
+    expect(isAbundantNumber(12)).toBe(true)
+  })
+
+  test('18 is an abundant number', () => {
+    expect(isAbundantNumber(18)).toBe(true)
+  })
+
+  test('20 is an abundant number', () => {
+    expect(isAbundantNumber(20)).toBe(true)
+  })
+
+  test('24 is an abundant number', () => {
+    expect(isAbundantNumber(24)).toBe(true)
+  })
+
+  test('1 is NOT an abundant number', () => {
+    expect(isAbundantNumber(1)).toBe(false)
+  })
+
+  test('9 is NOT an abundant number', () => {
+    expect(isAbundantNumber(9)).toBe(false)
+  })
+
+  test('6 is NOT an abundant number (perfect number)', () => {
+    expect(isAbundantNumber(6)).toBe(false)
+  })
+
+  test('11 is NOT an abundant number (prime)', () => {
+    expect(isAbundantNumber(11)).toBe(false)
+  })
+
+  test('throws TypeError for zero', () => {
+    expect(() => isAbundantNumber(0)).toThrow(TypeError)
+  })
+
+  test('throws TypeError for negative input', () => {
+    expect(() => isAbundantNumber(-12)).toThrow(TypeError)
+  })
+
+  test('throws TypeError for float input', () => {
+    expect(() => isAbundantNumber(12.5)).toThrow(TypeError)
+  })
+})