Mathematical puzzle to train the programmer's brain Q06 (modified version) Collatz's prediction

Problem summary

Find the number of even numbers less than 10000 that return to themselves by repeating the following operations.

--For the first time, multiply by 3 and add 1 ――From the second time onwards --For even numbers, divide n by 2. --For odd numbers, multiply n by 3 and add 1

Code

loopnums = []
for num in list(range(2, 10000, 2)):
    n = num * 3 + 1
    while True:
        if n % 2 == 0:
            n = n / 2
        else:
            n = n * 3 + 1
        if n == 1:
            break
        elif n == num:
            loopnums.append(num)
            break

print(loopnums)
print(len(loopnums))