Here's a program that is intended to count the length of a Collatz sequence recursively:

```
def odd_collatz ( n ):
return (3 * n) + 1
def even_collatz ( n ):
return int(n / 2)
def collatz_counter ( initialNumber, initialLength ):
length = initialLength
while True:
if initialNumber == 1:
return length
elif initialNumber != 1:
length += 1
if initialNumber % 2 == 0:
collatz_counter(even_collatz(initialNumber), length)
else:
collatz_counter(odd_collatz(initialNumber), length)
print(collatz_counter(13, 1)
```

The expected answer should be 10. However, the program gets stuck in an infinite loop. At the second to last step of the sequence `initalNumber`

equals 2. The program functions as expected: `collatz_counter`

is called using `even_collatz`

and the number 10.

The expected action of the next step would be to run `collatz_counter`

with an `initialNumber`

of 1 and an `initialLength`

of 10. What I would expect would happen is that the first if statement would evaluate to true, `collatz_counter`

should return `length`

and then exit. This is not, however, what happens:

What actually happens is that the function evaluates the first if statement, runs the `return length`

line, and then jumps to the line of code under `if initialNumber % 2...`

and the whole process repeats itself over and over and over in an infinite loop.

Any ideas as to why this might be happening?

You are mixing recursion and looping in a bit of an odd way. The problem is `while True:`

. Because you never return anything from within the loop there is nothing stopping it from going on forever. Your code reaches 1 then just keeps adding to the length. Here is a fixed version.

```
def odd_collatz ( n ):
return (3 * n) + 1
def even_collatz ( n ):
return int(n / 2)
def collatz_counter ( initialNumber, initialLength ):
length = initialLength
if initialNumber == 1:
return length
elif initialNumber != 1:
length += 1
if initialNumber % 2 == 0:
return collatz_counter(even_collatz(initialNumber), length)
else:
return collatz_counter(odd_collatz(initialNumber), length)
print(collatz_counter(13, 1))
```