I found a solution to a differential equation as a Fourier series written as

$\displaystyle X = a_0 + k \sum_{n \neq 0} \frac{1}{n} a_n e^{-in \tau}$

I've been having some trouble understanding the 1/n in the summand. Is this simply a way to underscore that n can't be 0 in the sum? I really don't know why the summand is written that way.

Thanks!

-Dan