168212023980domain: NAppears in sequencesNumber of permutations of 0..floor((n*3-1)/2) on even squares of an n X 3 array such that each row and column of even squares is increasing.at n=18A215287a(n) = (1/3)*(n+2)^2*(3*n+3)!/(n+2)!^3.at n=9A319578