collatz_sequence.py

def collatz_sequence(n):
    """
    Collatz conjecture: start with any positive integer n.Next term is obtained from the previous term as follows: 
    if the previous term is even, the next term is one half of the previous term. 
    If the previous term is odd, the next term is 3 times the previous term plus 1. 
    The conjecture states the sequence will always reach 1 regaardless of starting value n.
    Example:
    >>> collatz_sequence(43)
    [43, 130, 65, 196, 98, 49, 148, 74, 37, 112, 56, 28, 14, 7, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1]
    """
    sequence = [n]
    while n != 1:
        if n % 2 == 0:  # even number condition
            n //= 2
        else:
            n = 3 * n + 1
        sequence.append(n)
    return sequence


def main():
    n = 43
    sequence = collatz_sequence(n)
    print(sequence)
    print("collatz sequence from %d took %d steps." % (n, len(sequence)))


if __name__ == "__main__":
    main()