Compute 2018^2 - 2017^2 + 2016^2 - 2015^2 + ... + 4^2 - 3^2 + 2^2 - 1^2.
Sum them up as an arithmetic sequence:
sum_(n=1)^1009((2020 - 2 n)^2 - (2019 - 2 n)^2) = 2,037,171
1009/2 * [2*4035 + ( - 4*1008)] = S, solve for S
S =2,037, 171
