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# For each positive integer n, let S(n) denote the sum of the digits of n. How many three-digit n's are there such that

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For each positive integer n, let S(n) denote the sum of the digits of n. How many three-digit n's are there such that

$$n+S(n)+S(S(n))\equiv 0 \pmod{9}?$$

Sep 17, 2020
edited by PocketThePenguin  Sep 17, 2020