114526domain: NAppears in sequencesa(n) = K_4(n) = Sum_{k>=0} A090285(4,k)*2^k*binomial(n,k). a(n) = 2*(n^4+14*n^3+62*n^2+91*n+21)/3.at n=17A090296Number of ways to place zero or more nonadjacent 1,0 1,1 2,1 3,1 4,2 5,2 5,3 polyhexes in any orientation on a planar nXnXn triangular grid.at n=8A155334