create a main driver than repeatedly calls collatz() and determines the length of the returned list.

def collatz(number):
  if number % 2 == 0:
    return number // 2
  else:
    return 3 * number + 1

def driver(number):
  seq = [number]
  while number > 1:
    number = collatz(number)
    seq.append(number)
  return seq

driver(25)