a(n) is the constant term in expansion of Product_{k=1..n} (x^(2*k-1) + 1 + 1/x^(2*k-1)).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =3a(5) =9a(6) =21a(7) =49a(8) =117a(9) =295a(10) =761a(11) =1993a(12) =5261a(13) =14025a(14) =37699a(15) =102151a(16) =278587a(17) =764145a(18) =2106433a(19) =5832863a(20) =16217191a(21) =45255167a(22) =126708863a(23) =355848715a(24) =1002145705a(25) =2829479797a(26) =8007670701a(27) =22711890561a(28) =64547494347a(29) =183790615881