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MathNet 2005 — Part 03 Question 144

Math Olympiad Vault · MathNet 2005 — Part 03

Question 144

If $n$ is a positive integer, let $s(n)$ denote the sum of the digits of $n$. We say that $n$ is zesty if there exist positive integers $x$ and $y$ greater than 1 such that $x y = n$ and $s(x) s(y) = s(n)$. How many zesty two-digit numbers are there?