a(n) = T(2*n, n+1), T given by A027935.

Terms

a(0) =1a(1) =7a(2) =26a(3) =79a(4) =221a(5) =596a(6) =1581a(7) =4163a(8) =10926a(9) =28635a(10) =75001a(11) =196392a(12) =514201a(13) =1346239a(14) =3524546a(15) =9227431a(16) =24157781a(17) =63245948a(18) =165580101a(19) =433494395a(20) =1134903126a(21) =2971215027a(22) =7778742001a(23) =20365011024a(24) =53316291121