T(2n,n+2), T given by A026758.

Terms

a(0) =1a(1) =6a(2) =29a(3) =131a(4) =576a(5) =2505a(6) =10857a(7) =47081a(8) =204724a(9) =893766a(10) =3920310a(11) =17283214a(12) =76596745a(13) =341264480a(14) =1528405584a(15) =6880122182a(16) =31123426923a(17) =141456560459a(18) =645811464667