In [1]:

    

def collatz_sequence(n):
    while True:
        yield n
        if n % 2 == 0:
            n //= 2
        else:
            n = 3 * n + 1


    

In [2]:

    

for i, x in enumerate(collatz_sequence(9)):
    print(i, x)
    if x ==  1:
        break


    

    




0 9
1 28
2 14
3 7
4 22
5 11
6 34
7 17
8 52
9 26
10 13
11 40
12 20
13 10
14 5
15 16
16 8
17 4
18 2
19 1

In [3]:

    

def stopping_power(n):
    for i, n in enumerate(collatz_sequence(n)):
        if n == 1:
            return i


    

In [4]:

    

known_stopping_power = {
    27: 111,
    9: 19,
    97: 118,
    871: 178,
    6171: 261,
    77031: 350,
}

for n, s in known_stopping_power.items():
    assert stopping_power(n) == s, f'{n}, {s}, {stopping_power(n)}'