Did you mean `n*(n+1)`?  Putting symbols next to each other doesn't trigger multiplication in Python.

On a broader issue how can we help you set up a testing framework so that errors like this become obvious?  Ideally you should have a test somewhere that looks like the following

```Python
def test_CartanType_roots():
    ct = CartanType(5)
    assert ct.roots() == 30
```

I know that this sort of test seems trivial.  It's actually really helpful in isolating bugs down the line.  I can't tell you how many times the most trivial tests have saved my butt.