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Fermat numbers (Posted on 2017-07-13)

For any non-negative integer n define f(n)=2^(2^n)+1.
The above formula produces Fermat numbers i.e. 3,5,17,257 ...etc

Prove: Except the 1st term, the digital root of sequence's members are either 5 or 8, depending on parity of n.

No Solution Yet Submitted by Ady TZIDON

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