MathDB

Cono Sur Olympiad 2005, Problem 1

Source:

August 19, 2014

number theory proposednumber theory

Problem Statement

Let

a_n

be the last digit of the sum of the digits of

20052005...2005

, where the

2005

block occurs

n

times. Find

a_1 +a_2 + \dots +a_{2005}