feat: added hexagonal numbers 📏✏️

Author: SpiderMath

Maths/Series/HexagonalNumbers.ts

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+/**
+ * @function HexagonalNumbers
+ * @description To generate the requested number of hexagonal numbers
+ * @summary A hexagonal number, hₙ, is a figurate number which represents the number
+ * of distinct dots in a pattern of dots consisting of the outlines of regular
+ * hexagons with sides upto 'n' dots, when the hexagons are overlaid so that they share a common vertex
+ * 
+ * The nth hexagonal number, hₙ, is calculated by the formula:
+ * hₙ = n * (2n - 1)
+ * @see [Wikipedia](https://en.wikipedia.org/wiki/Hexagonal_number)
+ * @see [OEIS](https://oeis.org/A000384)
+ * @param {number} n - The number of Hexagonal numbers to generate
+ * @returns {number[]} - An array containing first 'n' hexagonal numbers
+ * @example HexagonalNumbers(10) = [ 1, 6, 15, 28, 45, 66, 91, 120, 153, 190 ]
+ * @example HexagonalNumbers(15) =  [ 1, 6, 15, 28, 45, 66, 91, 120, 153, 190, 231, 276, 325, 378, 435 ]
+ */
+export const HexagonalNumbers = (n: number): number[] => {
+  if (isNaN(n)) throw new Error('The input needs to be a number')
+  if (!Number.isInteger(n) || n < 0) throw new Error('The input needs to be a non-negative integer')
+  const hexagonalNumbers = []
+
+  for (let i = 1; i <= n; i++) {
+    hexagonalNumbers.push(i * (2 * i - 1))
+  }
+
+  return hexagonalNumbers
+}

Maths/Series/test/HexagonalNumbers.test.ts

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+import { HexagonalNumbers } from "../HexagonalNumbers";
+
+describe("HexagonalNumbers", () => {
+  it("should return the first 10 hexagonal numbers", () => {
+    expect(HexagonalNumbers(10)).toStrictEqual([1, 6, 15, 28, 45, 66, 91, 120, 153, 190]);
+  })
+
+  it("should return the first 5 hexagonal numbers", () => {
+    expect(HexagonalNumbers(5)).toStrictEqual([1, 6, 15, 28, 45])
+  })
+
+  it("should return zero hexagonal numbers", () => {
+    expect(HexagonalNumbers(0)).toStrictEqual([])
+  })
+})