From (-f,n-1) = c, the value of a,b and d increase by ONE every 2(n-1) cells, as you move from left to right in the grid.
From (e,n) = c, the value of a,b and d decrease by ONE every 2n cells, as you move from right to left in the grid.
These two rows are next to each other.
Any product of 2 primes will be divisible by 3 if you add either 2 or 4, or if you subtract 2 or 4.
Any product of 2 primes will be divisible by 5 if you…
Etc…
Remainders.
Patterns.
"Triangulation"