247945domain: NAppears in sequencesNumber of ways to build a contiguous building with n LEGO blocks of size 3 X 3 on top of a fixed block of the same size so that the building is symmetric after a rotation by 180 degrees.at n=7A123836a(n) = n^4 - 3*n^3 + 9*n^2 - 7*n + 5 (n>=1).at n=22A304162