You can put this solution on YOUR website! Prove that:
5^n+5^(n+1)+5^(n+2) we can split with 31
If you mean divisible by 31:
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5^n+5^(n+1)+5^(n+2)
n = 0 --> 1 + 5 + 25 = 31
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Other values of n, n>0, are 5^n times 5^n+5^(n+1)+5^(n+2) = 31*some number.
QED