a(n) = T(2n,n-4), T given by A026736.

Terms

a(0) =1a(1) =11a(2) =79a(3) =471a(4) =2535a(5) =12809a(6) =62067a(7) =292085a(8) =1345718a(9) =6102780a(10) =27343148a(11) =121359692a(12) =534632836a(13) =2341151646a(14) =10201950700a(15) =44278673806a(16) =191540714294a(17) =826265471868