a(n) = T(2*n+1,n+1), T given by A026998.

Terms

a(0) =1a(1) =8a(2) =26a(3) =73a(4) =196a(5) =518a(6) =1361a(7) =3568a(8) =9346a(9) =24473a(10) =64076a(11) =167758a(12) =439201a(13) =1149848a(14) =3010346a(15) =7881193a(16) =20633236a(17) =54018518a(18) =141422321a(19) =370248448a(20) =969323026a(21) =2537720633a(22) =6643838876a(23) =17393795998a(24) =45537549121a(25) =119218851368a(26) =312119004986a(27) =817138163593