MathDB
Wot n' Summation

Source: 2017 AIME I #3

March 8, 2017
2017 AIME I

Problem Statement

For a positive integer nn, let dnd_n be the units digit of 1+2+⋯+n1 + 2 + \dots + n. Find the remainder when ∑n=12017dn\sum_{n=1}^{2017} d_n is divided by 10001000.
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