Use the theory of congruence to prove that 17|(23n+1+3×52n+1) for all integer n≥1
(23n+1+3×52n+1)=2×8n+15×25n
=17×8n−1+374×25n−1+25n−1−8n−1
=25n−1−8n−1
=8n−1−8n−1 [since 25\equiv 8\mod 17)
=0\mod 17
0 is divisible by 17
Is this correct?
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