Source: *Fibonacci sequence algorithm in Javascript – Developers Writing – Medium*

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Probably one of the most famous algorithms ever, but still lot of people struggles when trying to find an efficient solution. Let me introduce you to the **Fibonacci sequence**.

### Statement

Given a number *N *return the index value of the Fibonacci sequence, where the sequence is:

1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, ...

After a quick look, you can easily notice that the pattern of the sequence is that each value is the sum of the **2 previous values**, that means that for N=5 → 2+3 or in maths:

F(n) = F(n-1) + F(n-2) ....