65714domain: NAppears in sequencesn*10^4-1, n*10^4-3, n*10^4-7 and n*10^4-9 are all prime.at n=17A064978a(0)=a(1)=0, a(2)=2; for n >= 3, a(n) = a(n-1) + 4*a(n-3).at n=18A122946Number of ways to place zero or more nonadjacent 0,0 1,0 2,1 2,2 3,0 3,1 4,0 4,2 polyhexes in any orientation on a planar nXnXn triangular grid.at n=9A155404