User:Mankeyrabbit/sandbox

What you're saying is:

$$\displaystyle\sum ab$$

But a, and b; what are they indexed over? are they constant in the sum?

E.g.:

$$\displaystyle\sum_{a}\sum_{b}ab$$

$$\displaystyle\sum_{k=0}^n ab$$

Where k is referenced by both a and b, for example:

$$\displaystyle a = 2k, b = 3k$$

$$s(n) = \displaystyle\sum_{k=0}^nu(k)$$