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The Last Two Digits (
Posted on 20130904
)
What are the last two digits of (1+5^(2n+1))/6?
Note that n is assumed to be any positive integer.
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Submitted by
Danish Ahmed Khan
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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 20130904 10:30:41
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