T(2n+3,n), array T as in A055216.

Terms

a(0) =1a(1) =5a(2) =21a(3) =78a(4) =274a(5) =927a(6) =3061a(7) =9933a(8) =31824a(9) =100972a(10) =317942a(11) =995088a(12) =3099105a(13) =9612735a(14) =29715525a(15) =91595391a(16) =281643480a(17) =864189486a(18) =2646805668a(19) =8093543439a(20) =24713953515a(21) =75370741506a(22) =229604257846a(23) =698754428388