olymmath

BALTIC-WAY 1998 Problem 20

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We say that an integer mm covers the number 1998 if 1,9,9,81,9,9,8 appear in this order as digits of mm. (For instance, 1998 is covered by 215993698 but not by 213326798 .) Let k(n)k(n) be the number of positive integers that cover 1998 and have exactly nn digits (n⩾5)(n \geqslant 5), all different from 0 . What is the remainder of k(n)k(n) in division by 8 ?

Dataset text NuminaMath olympiads. Quoted with source.

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