fibonacci direct formula code example

Example 1: fibonacci sequence

0, 1, 1, 2, 3, 5, 8, 13, 21, 34, ...

Example 2: Tribonacci

const tribonacci = (signature,n) => {
    let orgArr = [...signature]
    let len = orgArr.length
    let arr = []
    if(n === 0){
        return []
    }else if(n < 3){
        orgArr = orgArr.slice(0, n)
    }else{
        for(let i = len; i < n; i++){
            if(i <= n){
                arr = orgArr.slice(-3)
                let nextValue = arr.reduce((acc, curr) => acc + curr, 0)
                orgArr.push(nextValue)
                arr = []
            }else{
                return 1
            }
        }
    }
    return orgArr
}