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

Terms

a(0) =1a(1) =19a(2) =101a(3) =370a(4) =1148a(5) =3278a(6) =8967a(7) =23993a(8) =63483a(9) =167040a(10) =438346a(11) =1148844a(12) =3009181a(13) =7879855a(14) =20631713a(15) =54016798a(16) =141420392a(17) =370246298a(18) =969320643a(19) =2537718005a(20) =6643835991a(21) =17393792844a(22) =45537545686a(23) =119218847640a(24) =312119000953a(25) =817138159243