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Digit sum

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July 5, 2015
digit sum

Problem Statement

Let S(n)S(n) be the sum of digits for any positive integer n (in decimal notation). Let N=∑k=102003102004−1S(k)N=\displaystyle\sum_{k=10^{2003}}^{10{^{2004}-1}} S(k). Determine S(N)S(N).
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