a(n) = A074829(2*n-1, n).

Terms

a(0) =1a(1) =2a(2) =8a(3) =30a(4) =114a(5) =436a(6) =1676a(7) =6468a(8) =25040a(9) =97190a(10) =378050a(11) =1473254a(12) =5750390a(13) =22476090a(14) =87958306a(15) =344593314a(16) =1351330642a(17) =5303953012a(18) =20834616860a(19) =81900891372a(20) =322168053848