a(n) = A047080(2*n, n+1).

Terms

a(0) =1a(1) =3a(2) =8a(3) =24a(4) =75a(5) =237a(6) =755a(7) =2421a(8) =7804a(9) =25264a(10) =82081a(11) =267487a(12) =873970a(13) =2862038a(14) =9391137a(15) =30869167a(16) =101627704a(17) =335049772a(18) =1106003560a(19) =3655124296a(20) =12092095945a(21) =40042017815a(22) =132712302538a(23) =440207294382