If , where for all and ,…

MATHEMATICS · Single correct · AoPS · Mathematics · Functions · Functions

Problem

If ∑k=1nf(a+k)=16(2n−1)\sum_{k=1}^n f(a+k)=16(2^n-1), where f(x+y)=f(x)f(y)f(x+y)=f(x)f(y) for all x,y∈Nx,y\in\mathbb{N} and f(1)=2f(1)=2, then f(a)=f(a)= (a) 8 (b) 6 (c) 4 (d) 2

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