def collatz ( n ):

  if ( n == 1 ):
    Tn = 1
  elif ( n % 2 == 0 ):
    Tn = int ( n / 2 )
  else:
    Tn = 3 * n + 1

  return Tn

def collatz_test ( ):

  print ( '' )
  print ( 'collatz_test():' )
  print ( '  Print the next element of a Collatz sequence:' )

  n = 7
  while ( n != 1 ):
    print ( ' ', n, end = '' )
    n = collatz ( n )

  print ( ' 1' )

  return

if ( __name__ == "__main__" ):
  collatz_test ( )