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

Terms

a(0) =1a(1) =11a(2) =51a(3) =176a(4) =530a(5) =1490a(6) =4043a(7) =10773a(8) =28445a(9) =74770a(10) =196116a(11) =513876a(12) =1345861a(13) =3524111a(14) =9226935a(15) =24157220a(16) =63245318a(17) =165579398a(18) =433493615a(19) =1134902265a(20) =2971214081a(21) =7778740966a(22) =20365009896a(23) =53316289896a(24) =139583861065a(25) =365435294675a(26) =956722024443