a(n) = 3^n * Sum_{i=1..n} i^3/3^i.

Terms

a(0) =1a(1) =11a(2) =60a(3) =244a(4) =857a(5) =2787a(6) =8704a(7) =26624a(8) =80601a(9) =242803a(10) =729740a(11) =2190948a(12) =6575041a(13) =19727867a(14) =59186976a(15) =177565024a(16) =532699985a(17) =1598105787a(18) =4794324220a(19) =14382980660a(20) =43148951241a(21) =129446864371a(22) =388340605280