\((1+2+3+...+n)+(2+3+...+n)+...+((n-1)+n)+n=?\)
Math without words 
Formula 12
Sponsors:
Created on: 2007
Last update: 2023-05-04 11:36:21+0100
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.