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
  elif number % 2 == 1:
    return 3 * number + 1

print('Enter number:')
try:
  n = int(input())
  print(n)
except ValueError:
  print('You must enter an integer')