perplexus.info :: Just Math : The Last Two Digits

The Last Two Digits (Posted on 2013-09-04)

What are the last two digits of (1+5^(2n+1))/6?
Note that n is assumed to be any positive integer.

No Solution Yet Submitted by Danish Ahmed Khan

Rating: 4.0000 (1 votes)

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answer - spoiler

| Comment 1 of 3

the last two digits are 21

Proof 1- by induction.

Proof 2- by observing that the odd powers of 5 terminate by 125 or 625.

Posted by Ady TZIDON on 2013-09-04 10:30:41

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