Kvant Math Problem 1270

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kvantmathematicsolympiad

Verified: no
Verdicts: SKIP + SKIP
Solve time: 8m39s
Source on kvant.digital

Problem

Prove that if the last digit of the decimal representation of the number $m$ is 5, then $12^m+9^m+8^m+6^m$ is divisible by 1991.

N. B. Vasiliev