a(n) = (1/2)*A291228(n).

Terms

a(0) =1a(1) =3a(2) =9a(3) =28a(4) =85a(5) =261a(6) =797a(7) =2440a(8) =7461a(9) =22827a(10) =69821a(11) =213588a(12) =653345a(13) =1998573a(14) =6113529a(15) =18701072a(16) =57205769a(17) =174990195a(18) =535287793a(19) =1637423756a(20) =5008812525a(21) =15321754293a(22) =46868623381a(23) =143369215128a(24) =438560602669