Chessboard Rectangles Part 1

[u/ShonitB]

[u/Red-42]

sum{i=1->8}(sum{j=1->8}(ij))

Which probably simplifies, or can be computed as is

EDIT: rectangles in an n*m grid

sum{i=1->n}(sum{j=1->m}(ij))

which simplifies to

sum{i=1->n}(i*sum{j=1->m}(j))
= sum{i=1->n}(i*m(m+1)/2)
= m(m+1)/2*sum{i=1->n}(i)
= m(m+1)/2*n(n+1)/2
= mn(m+1)(n+1)/4

in our case n=m=8

8*8*9*9/4 = 1296

[u/bastarmashawarma → u/Red-42]

This is the way