MG> we can guess that triangle: https://oeis.org/A123706 MG> can be defined in terms of the Moebius function as: MG> A123706(n,k) = moebius(n/k)- moebius(n/(k+1)) MG> where moebius(n) is zero if n is not an integer. This is brilliant and exactly what we need here. Bravo Mats! Peter