Possible Duplicate:
Solving a Recurrence Relation/Equation, is there more than 1 way to solve this?
How do I find an explicit formula for $a_n$ given $a_0 = 3$ and $a_{n+1} = 2a_n + 1$. I'm guessing it's probably related to the formula for first $n$ terms of a geometric series. Any help is appreciated