Math Help - Proof

I can't find the topic I made.. ugh.

Any way I'm trying to prove always ends in the digits .

I almost had it.. something like:

. . . this doesn't quite work. I have to tweek that somehow to show it.

Anyone? I know the proof is similar to what I have. I just can't tweek it to get integers x = 1, 2, ... to satisfy that and include all the powers of 5 to show that you get something (something like 1000 + 100 + 25) and hence will always have 00 + 25 which completes the proof.

Hello,

You can prove that always ends by 25 for

Do it by induction if you want to
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It's ok for x=2

Assume ends up by 25, that is to say , where k is a (positive) integer.



, which obviously ends up by 25