MathDB

N and N^2 both end in the same four digits

Source: 2019 Dürer Math Competition Finals Day2 E+8 https://artofproblemsolving.com/community/c1621835_2019_

January 5, 2022

number theoryDigitslast digits

Problem Statement

Let

N

be a positive integer such that

N

and

N^2

both end in the same four digits

\overline{abcd}

, where

a \ne 0

. What is the four-digit number

\overline{abcd}