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For any positive integer $n$, $d_n$ it the last digit of $(1+2+\dots+n)$. What is the reminder when $\sum_{n=1}^{2017} d_n$ is divided by $1000$?
Source:MAA
Number Theory
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For any positive integer $n$, $d_n$ it the last digit of $(1+2+\dots+n)$. What is the reminder when $\sum_{n=1}^{2017} d_n$ is divided by $1000$?
Source:MAA