Cell i of row j contains n elements of an arithmetic progression, with common difference of j.
If i and j have a GCD != 1, they are not coprime, so they share a factor p, as do all numbers in the sequence, so they cannot be prime
Otherwise it's very likely there's at least one prime
If j is prime every column i is coprime with it, so it's going to be black
Cell i of row j contains n elements of an arithmetic progression, with common difference of j. If i and j have a GCD != 1, they are not coprime, so they share a factor p, as do all numbers in the sequence, so they cannot be prime
Otherwise it's very likely there's at least one prime
If j is prime every column i is coprime with it, so it's going to be black