a(n) = T(2n+1,n+1), T given by A026736.

Terms

a(0) =1a(1) =3a(2) =10a(3) =36a(4) =136a(5) =530a(6) =2109a(7) =8515a(8) =34739a(9) =142817a(10) =590537a(11) =2452639a(12) =10221505a(13) =42714623a(14) =178888442a(15) =750500716a(16) =3153137436a(17) =13263180550a(18) =55844218906a(19) =235323138044a(20) =992316962382