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Sum of gcd of n and 2019-n.

Source: RMO maharashtra and goa 2019 P1

November 10, 2019

number theorygreatest common divisor

Problem Statement

For each

n\in\mathbb{N}

let

d_n

denote the gcd of

n

and

(2019-n)

. Find value of

d_1+d_2+\cdots d_{2018}+d_{2019}