It is given that $a_n$ is generated by the following function:
$${1+6x} \over {(1+5x)(1-x)}$$
What is the generating function of:
$$\left\{ {\matrix{
{{a_n},\mathbb{N}_{even}} \cr
{0,\mathbb{N}_{odd}} \cr
} } \right.$$
I'm guessing it's a technical issue, which i am lacking of.
I'll be glad for an explanation.
Thanks!
Hint: $\dfrac{f(x)+f(-x)}{2}$.