Power and Modulo

Problem #202

Power and Modulo

$F(k) = 5^k$ mod $(10^{k'})$ where $k' = k$ mod $6$

Let $S(N)$ be the sum of $F(k)$ for all $1 \leq k \leq N$ .

Find $S(10^{18})$ mod $10^9+7$ .

Contributed by Shivansh Arora

Solved by 92 users

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