function tribonacci(signature,n){
for (var i = 0; i < n-3; i++) { // iterate n times
signature.push(signature[i] + signature[i+1] + signature[i+2]); // add last 3 array items and push to trib
}
return signature.slice(0, n); //return trib - length of n
}
function tribonacci(s,n){
var arr = [];
for(var i=0; i<n; i++) {
arr.push((i<3) ? s[i] : arr[i-1]+arr[i-2]+arr[i-3]);
}
return arr;
}