I have been trying to solve this python problem involving permutations. For example, this is what should happen when I call the function:

combinations(2, 3) ➞ 6

combinations(3, 7, 4) ➞ 84

combinations(2, 3, 4, 5) ➞ 120

I don't know why but when I call it (down below) it returns 2 for some reason. I know computers just follow instructions so there must be something wrong with my code. I don't know what though, please someone tell me! Thank you!

```
def combinations(*items):
    permu = []
    for i in range(0, len(items)):
        if i == 0:
            permu.append(items[i]*items[i+1])
        else:
            permu.append(items[i]*permu[i-1])

    return sum(permu)

print(combinations(1,2,3,4))

```