MathDB
Sum of digits

Source: Brazil MO 2018 Grades 8 and 9

November 16, 2018
number theory

Problem Statement

Let S(n)S(n) be the sum of digits of nn. Determine all the pairs (a,b)(a, b) of positive integers, such that the expression S(an+b)āˆ’S(n)S(an + b) - S(n) has a finite number of values, where nn is varying in the positive integers.
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