merge: Added LucasSeries Implementation (TheAlgorithms#808)

* Added LucasSeries

* Added more tests and renamed function

* Changed RangeError to TypeError

Author: SpiderMath

Maths/LucasSeries.js

@@ -0,0 +1,33 @@
+/*
+  Program to get the Nth Lucas Number
+  Article on Lucas Number: https://en.wikipedia.org/wiki/Lucas_number
+  Examples:
+    > loopLucas(1)
+    1
+    > loopLucas(20)
+    15127
+    > loopLucas(100)
+    792070839848372100000
+*/
+
+/**
+ * @param {Number} index The position of the number you want to get from the Lucas Series
+ */
+function lucas (index) {
+  // index can't be negative
+  if (index < 0) throw new TypeError('Index cannot be Negative')
+
+  // index can't be a decimal
+  if (Math.floor(index) !== index) throw new TypeError('Index cannot be a Decimal')
+
+  let a = 2
+  let b = 1
+  for (let i = 0; i < index; i++) {
+    const temp = a + b
+    a = b
+    b = temp
+  }
+  return a
+}
+
+export { lucas }

Maths/test/LucasSeries.test.js

@@ -0,0 +1,15 @@
+import { lucas } from '../LucasSeries'
+
+describe('Nth Lucas Number', () => {
+  it('should return the 20th Lucas Number', () => {
+    expect(lucas(20)).toBe(15127)
+  })
+
+  it('should return the 20th Lucas Number', () => {
+    expect(lucas(0)).toBe(2)
+  })
+
+  it('should return the 20th Lucas Number', () => {
+    expect(lucas(100)).toBe(792070839848372100000)
+  })
+})