feat: Add hexagonal numbers

DIRECTORY.md

@@ -1,41 +1,50 @@
 
 ## Ciphers
-  * [Xor Cipher](https://github.com/TheAlgorithms/TypeScript/blob/master/ciphers/xor_cipher.ts)
+  * [Xor Cipher](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/ciphers/xor_cipher.ts)
 
 ## Data Structures
-  * [Stack](https://github.com/TheAlgorithms/TypeScript/blob/master/data_structures/stack.ts)
+  * [Stack](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/data_structures/stack.ts)
 
 ## Dynamic Programming
-  * [Knapsack](https://github.com/TheAlgorithms/TypeScript/blob/master/dynamic_programming/knapsack.ts)
+  * [Knapsack](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/dynamic_programming/knapsack.ts)
 
 ## Maths
-  * [Absolute Value](https://github.com/TheAlgorithms/TypeScript/blob/master/maths/absolute_value.ts)
-  * [Aliquot Sum](https://github.com/TheAlgorithms/TypeScript/blob/master/maths/aliquot_sum.ts)
-  * [Armstrong Number](https://github.com/TheAlgorithms/TypeScript/blob/master/maths/armstrong_number.ts)
-  * [Binary Convert](https://github.com/TheAlgorithms/TypeScript/blob/master/maths/binary_convert.ts)
-  * [Calculate Mean](https://github.com/TheAlgorithms/TypeScript/blob/master/maths/calculate_mean.ts)
-  * [Degrees To Radians](https://github.com/TheAlgorithms/TypeScript/blob/master/maths/degrees_to_radians.ts)
-  * [Digit Sum](https://github.com/TheAlgorithms/TypeScript/blob/master/maths/digit_sum.ts)
-  * [Factorial](https://github.com/TheAlgorithms/TypeScript/blob/master/maths/factorial.ts)
-  * [Fibonacci](https://github.com/TheAlgorithms/TypeScript/blob/master/maths/fibonacci.ts)
-  * [Find Min](https://github.com/TheAlgorithms/TypeScript/blob/master/maths/find_min.ts)
-  * [Greatest Common Factor](https://github.com/TheAlgorithms/TypeScript/blob/master/maths/greatest_common_factor.ts)
-  * [Is Divisible](https://github.com/TheAlgorithms/TypeScript/blob/master/maths/is_divisible.ts)
-  * [Is Even](https://github.com/TheAlgorithms/TypeScript/blob/master/maths/is_even.ts)
-  * [Is Leap Year](https://github.com/TheAlgorithms/TypeScript/blob/master/maths/is_leap_year.ts)
-  * [Is Odd](https://github.com/TheAlgorithms/TypeScript/blob/master/maths/is_odd.ts)
-  * [Lowest Common Multiple](https://github.com/TheAlgorithms/TypeScript/blob/master/maths/lowest_common_multiple.ts)
-  * [Perfect Square](https://github.com/TheAlgorithms/TypeScript/blob/master/maths/perfect_square.ts)
-  * [Radians To Degrees](https://github.com/TheAlgorithms/TypeScript/blob/master/maths/radians_to_degrees.ts)
-  * [Sieve Of Eratosthenes](https://github.com/TheAlgorithms/TypeScript/blob/master/maths/sieve_of_eratosthenes.ts)
+  * [Absolute Value](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/absolute_value.ts)
+  * [Aliquot Sum](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/aliquot_sum.ts)
+  * [Armstrong Number](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/armstrong_number.ts)
+  * [Binary Convert](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/binary_convert.ts)
+  * [Calculate Mean](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/calculate_mean.ts)
+  * [Degrees To Radians](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/degrees_to_radians.ts)
+  * [Digit Sum](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/digit_sum.ts)
+  * [Factorial](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/factorial.ts)
+  * [Fibonacci](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/fibonacci.ts)
+  * [Find Min](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/find_min.ts)
+  * [Greatest Common Factor](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/greatest_common_factor.ts)
+  * [Is Divisible](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/is_divisible.ts)
+  * [Is Even](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/is_even.ts)
+  * [Is Leap Year](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/is_leap_year.ts)
+  * [Is Odd](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/is_odd.ts)
+  * [Lowest Common Multiple](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/lowest_common_multiple.ts)
+  * [Perfect Square](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/perfect_square.ts)
+  * [Radians To Degrees](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/radians_to_degrees.ts)
+  * Series
+    * [Hexagonal Numbers](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/series/hexagonal_numbers.ts)
+    * Test
+      * [Hexagonal Numbers.Test](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/series/test/hexagonal_numbers.test.ts)
+  * [Sieve Of Eratosthenes](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/maths/sieve_of_eratosthenes.ts)
+
+## Other
+  * [Parse Nested Brackets](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/other/parse_nested_brackets.ts)
+  * Test
+    * [Parse Nested Brackets.Test](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/other/test/parse_nested_brackets.test.ts)
 
 ## Search
-  * [Binary Search](https://github.com/TheAlgorithms/TypeScript/blob/master/search/binary_search.ts)
-  * [Linear Search](https://github.com/TheAlgorithms/TypeScript/blob/master/search/linear_search.ts)
+  * [Binary Search](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/search/binary_search.ts)
+  * [Linear Search](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/search/linear_search.ts)
 
 ## Sorts
-  * [Bubble Sort](https://github.com/TheAlgorithms/TypeScript/blob/master/sorts/bubble_sort.ts)
-  * [Gnome Sort](https://github.com/TheAlgorithms/TypeScript/blob/master/sorts/gnome_sort.ts)
-  * [Insertion Sort](https://github.com/TheAlgorithms/TypeScript/blob/master/sorts/insertion_sort.ts)
-  * [Merge Sort](https://github.com/TheAlgorithms/TypeScript/blob/master/sorts/merge_sort.ts)
-  * [Quick Sort](https://github.com/TheAlgorithms/TypeScript/blob/master/sorts/quick_sort.ts)
+  * [Bubble Sort](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/sorts/bubble_sort.ts)
+  * [Gnome Sort](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/sorts/gnome_sort.ts)
+  * [Insertion Sort](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/sorts/insertion_sort.ts)
+  * [Merge Sort](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/sorts/merge_sort.ts)
+  * [Quick Sort](https://github.com/TheAlgorithms/TypeScript/blob/HEAD/sorts/quick_sort.ts)

maths/series/hexagonal_numbers.ts

@@ -0,0 +1,27 @@
+/**
+ * @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/hexagonal_numbers.test.ts

@@ -0,0 +1,15 @@
+import { HexagonalNumbers } from "../hexagonal_numbers";
+
+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([])
+  })
+})