Number theory · Repdigits · Triangular numbers · Last digit analysis · Coprime factorisation · Powers of two and five
For some integer \(n > 3\), all the digits of the number
\[ 1 + 2 + \cdots + n \]
are equal to one another. Which digit can this be?
Sign in to check answers, open hints, read the full solution, and track your progress. Statements are always free.
Serbian Republic Competition (Republicko takmicenje) 2006, high school grade I, category A, problem 5. Organized by the Mathematical Society of Serbia (DMS). Source