LinearRecursion
2015

Problem - 2163
The Fibonacci numbers are defined by $F_1=1, F_2=1$, and $F_n=F_{n-1} + F_{n-2}$ for $n=3, 4, \cdots$. Find and prove a formula for the sum of the first $n$ Fibonacci numbers, i.e. $F_1 + F_2 + \cdots +F_n$.