L = [1,2,3,4]; x = 2
k = len(L)-1;  y = L[k]
print('L =', L)
print(k, y)
while k > 0:
    k = k - 1
    y = y*x + L[k]
    print(k, y)
print(y)

# with a for loop

k = len(L)-1; y = L[k]
print(k, y)
print(list(range(len(L)-2,-1,-1)))
for k in range(len(L)-2,-1,-1):
    y = y*x + L[k]
    print(k, y)
print(y)