The Fibonacci sequence is a series of numbers where each number in the sequence is the sum of the two preceding numbers. This sequence begins with 0 and 1. In mathematics, the Fibonacci numbers form the sequence, where numbers (n) are greater than 1 (n > 1).

To better understand how the fibonacci numbers are created in the sequence, view the below equation for generating any number in the fibonacci sequence.

Fn = Fn-1 + Fn-2

## Generate the sequence

Now that the underlying mathematical equation for generating the Fibonacci sequence is known, let's write a JavaScript function to create it.

``function fibonacciSeq(n) {    let arr = [0, 1];    let num = 0;    for (var i = 1; i < n; i++) {        num = arr[i] + arr[i-1];        arr.push(num);    }    return arr;}``

The above function `fibonacciSeq` accepts one parameter, the amount of fibonacci numbers to generate in the sequence and returns an array containing the fibonacci sequence. For example, passing in `n = 7` will generate the following sequence:

``console.log(fibonacciSeq(7));// [0, 1, 1, 2, 3, 5, 8, 13]``

### Sum the sequence

You can sum the values in a fibonacci sequence fairly quickly with `reduce`. Using a `for` loop would also work (and in some cases is more performant than `reduce`).

``function fibonacciSum(n) {    let arr = [0, 1];    let num = 0;    for (var i = 1; i < n; i++) {        num = arr[i] + arr[i-1];        arr.push(num);    }    return arr.reduce((a, b) => a + b);}``