a = (2 + 4 + .. + 4034)×(1/1×2 + 1/2×3 + .. + 1/2016×2017 + 1/2017×2018)
= 2(1 + 2 + .. + 2017)×(1 - 1/2 + 1/2 - 2/3 + .. + 1/2016 1/2017 + 1/2017 - 1/2018)
= (2×2017×2018 : 2)(1 - 1/2018)
= 2017×2018×(2018 - 1)/2018
= 2017×2018×2017/2018
= 2017×2017
= 2017²