Posted by **Miley** on Friday, December 27, 2013 at 4:08pm.

Suppose that for any integer n,

f(n)= (n-1). if n is even;

f(n)= (2n). if n is odd.

If k ∈ N, and f (f (f(k))) = 21, find the sum of the digits in k

I really don't get this means. (∈)

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