How can we calculate the formula for the following series?
$\frac13+\frac29+\frac{1}{27}+\frac{2}{81}+\frac{1}{243}+\frac{2}{729}+\ldots$
I'm not quite sure what type of series it is anyway. It doesn't look geometric. Is there any strategy/procedure to follow in order to calculate the formula for a series of numbers?