Thanks AA.
I can verify once I'm at a desktop.
Now, quick reminder on triangular numbers and the construction of the grid.
Column 0.
The values of a[t] at 0,0 are twice the square numbers.
The values of d[t] at 0,0 are 4 multiples by the triangular numbers. All other cells at row 1 can be constructed from these values by adding to them or subtracting from them.