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1 + 2 + 3 + .. + n = three-digit number with identical digits.

Source: Polish MO second round 1955 p2

August 29, 2024
number theoryDigits

Problem Statement

Find the natural number n n knowing that the sum 1+2+3+…+n 1 + 2 + 3 + \ldots + n is a three-digit number with identical digits.
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