T(2n+1,n+2), T given by A026780.

Terms

a(0) =1a(1) =6a(2) =30a(3) =144a(4) =687a(5) =3296a(6) =15972a(7) =78294a(8) =388320a(9) =1947910a(10) =9875566a(11) =50560246a(12) =261177401a(13) =1360112590a(14) =7134802722a(15) =37673830960a(16) =200106632766