Number of 3 X n 0..2 arrays with rows nondecreasing and antidiagonals unimodal.

Terms

a(0) =27a(1) =216a(2) =868a(3) =2661a(4) =6815a(5) =15340a(6) =31324a(7) =59267a(8) =105461a(9) =178416a(10) =289332a(11) =452617a(12) =686451a(13) =1013396a(14) =1461052a(15) =2062759a(16) =2858345a(17) =3894920a(18) =5227716a(19) =6920973a(20) =9048871a(21) =11696508a(22) =14960924a(23) =18952171a(24) =23794429a(25) =29627168a(26) =36606356a(27) =44905713a(28) =54718011