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Add fibonnaci sequence closed form function (trekhleb#130)

* Add fibonnaci sequence closed form function * Revert package-lock.json

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	`1`	`+import fibonacciClosedForm from '../fibonacciClosedForm';`
	`2`	`+`
	`3`	`+describe('fibonacciClosedForm', () => {`
	`4`	`+ it('should calculate fibonacci correctly', () => {`
	`5`	`+ expect(fibonacciClosedForm(1)).toBe(1);`
	`6`	`+ expect(fibonacciClosedForm(2)).toBe(1);`
	`7`	`+ expect(fibonacciClosedForm(3)).toBe(2);`
	`8`	`+ expect(fibonacciClosedForm(4)).toBe(3);`
	`9`	`+ expect(fibonacciClosedForm(5)).toBe(5);`
	`10`	`+ expect(fibonacciClosedForm(6)).toBe(8);`
	`11`	`+ expect(fibonacciClosedForm(7)).toBe(13);`
	`12`	`+ expect(fibonacciClosedForm(8)).toBe(21);`
	`13`	`+ expect(fibonacciClosedForm(20)).toBe(6765);`
	`14`	`+ expect(fibonacciClosedForm(30)).toBe(832040);`
	`15`	`+ expect(fibonacciClosedForm(50)).toBe(12586269025);`
	`16`	`+ expect(fibonacciClosedForm(70)).toBe(190392490709135);`
	`17`	`+ expect(fibonacciClosedForm(71)).toBe(308061521170129);`
	`18`	`+ expect(fibonacciClosedForm(72)).toBe(498454011879264);`
	`19`	`+ expect(fibonacciClosedForm(73)).toBe(806515533049393);`
	`20`	`+ expect(fibonacciClosedForm(74)).toBe(1304969544928657);`
	`21`	`+ expect(fibonacciClosedForm(75)).toBe(2111485077978050);`
	`22`	`+ });`
	`23`	`+});`

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	`1`	`+/**`
	`2`	`+ * Calculate fibonacci number at specific position using closed form function.`
	`3`	`+ *`
	`4`	`+ * @param n n-th number of fibonacci sequence (must be number from 1(inclusive) to 75(inclusive))`
	`5`	`+ * @return {number}`
	`6`	`+ */`
	`7`	`+export default function fibonacciClosedForm(n) {`
	`8`	`+ const sqrt5 = Math.sqrt(5);`
	`9`	`+ const phi = (1 + sqrt5) / 2;`
	`10`	`+ return Math.floor((phi ** n) / sqrt5 + 0.5);`
	`11`	`+}`

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