IMO Shortlist 1971 problem 6
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Let
be a natural number. Find a way to assign natural numbers to the vertices of a regular
-gon such that the following conditions are satisfied:
(1) only digits
and
are used;
(2) each number consists of exactly
digits;
(3) different numbers are assigned to different vertices;
(4) the numbers assigned to two neighboring vertices differ at exactly one digit.


(1) only digits


(2) each number consists of exactly

(3) different numbers are assigned to different vertices;
(4) the numbers assigned to two neighboring vertices differ at exactly one digit.
Izvor: Međunarodna matematička olimpijada, shortlist 1971