T(2n,n-1), T given by A026568.

Terms

a(0) =1a(1) =2a(2) =12a(3) =38a(4) =200a(5) =701a(6) =3682a(7) =13294a(8) =70665a(9) =258430a(10) =1388002a(11) =5114572a(12) =27682135a(13) =102539204a(14) =558172494a(15) =2075658454a(16) =11348521989a(17) =42330184638