Number of 3Xn 0..2 arrays with rows and antidiagonals unimodal.

Terms

a(0) =27a(1) =729a(2) =9515a(3) =76092a(4) =440628a(5) =2026448a(6) =7829639a(7) =26375691a(8) =79507149a(9) =218578373a(10) =555979549a(11) =1323191288a(12) =2972776392a(13) =6350443334a(14) =12975277251a(15) =25482263325a(16) =48302292951a(17) =88682057873a(18) =158180868607a(19) =274824912452a(20) =466153399196