a(n) = A129151(n) / 27.

Terms

a(0) =3a(1) =4a(2) =8a(3) =20a(4) =44a(5) =92a(6) =188a(7) =380a(8) =856a(9) =2148a(10) =5024a(11) =17616a(12) =58768a(13) =176320a(14) =755904a(15) =3305920a(16) =13885184a(17) =69634816a(18) =348174336a(19) =2385273856a(20) =14652403712a(21) =102566830080a(22) =849285738496