ABSTRACT
For the obvious geometric interpretation of the sum Δ r of first r natural numbers, i.e. Δ r = 1 + 2 + 3 + ⋯ + r = r ( r + 1 ) 2 , https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203747018/bef25d74-ef02-4914-ac4f-27ec89fc30ac/content/eq522.tif"/>
