MathDB
RMO 2023 P3

Source:

October 29, 2023
number theory

Problem Statement

For any natural number nn, expressed in base 10 , let s(n)s(n) denote the sum of all its digits. Find all natural numbers mm and nn such that m<nm<n and (s(n))2=m and (s(m))2=n. (s(n))^2=m \text { and }(s(m))^2=n .