(n²- n) : 2018
n=2019+2•(1+2+3+....+2018)
n=2019+2•2018•2019/2
n=2019+2018•2019
n=2019•2019
n=2019²
(n²- n) : 2018 =
=[(2019²)²-2019²]:2018
=(2019²-2019) (2019²+2019):2018
=2019(2019-1)(2019²+2019):2018
=2019•2018•(2019²+2019):2018
=2019• (2019²+2019) rest 0
=2019²·2020, rest 0
