# Recursion 2

Algebra Level pending

Let $$a_{0}=1$$, $$a_{1}=2$$ and $$a_{n}=2 \times a_{n-1}$$ be an $$n^{\text{th}}$$ term of a sequence where $$n>1$$ and let

$S=\sum_{n=0}^{20} {a_{n}}$

Compute $$S \bmod {2015}$$.

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