object Tribonacci {
def helper[T : Numeric](sign:List[T],n:Int,answ:List[T], i:Int): List[T] =
  {
    val l = sign.sum
    val answ1=(answ.concat(List(l)))
    val sign1 = List(sign(1),sign(2),answ1.last)
    if(i<n-4) helper(sign1, n, answ1, i+1)
    else answ1
  }
 def tribonacci[T : Numeric](signature: List[T], n: Int): List[T] = {
    if(n==0) List()
    else if(n<3)List(signature(n-1))
    else helper(signature, n, signature,0)
  }}