∑ Share definition Flag sigma a greek letter often used in math as representation of summary operation how would you write sum from 1 to 1000, without typing 1000 numbers? I would use sigma ∑ notation tex\sum_{1}^{1000} i/tex ∑ by seledrim May 15, 2016 0 0 Get merch Get the ∑ mug. Buy Now — $32.95 See more merch