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interesting numbers, remainder 2 under division by 4, in reverse order also

Source: 2018 Ecuador Juniors (OMEC) L2 p5

October 25, 2022
number theoryremainderDigits

Problem Statement

We call a positive integer interesting if the number and the number with its digits written in reverse order both leave remainder 22 in division by 44. a) Determine if 20182018 is an interesting number. b) For every positive integer nn, find how many interesting nn-digit numbers there are.
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