a(n) = (2^A002326(n)-1)/(2*n+1).

Terms

a(0) =1a(1) =1a(2) =3a(3) =1a(4) =7a(5) =93a(6) =315a(7) =1a(8) =15a(9) =13797a(10) =3a(11) =89a(12) =41943a(13) =9709a(14) =9256395a(15) =1a(16) =31a(17) =117a(18) =1857283155a(19) =105a(20) =25575a(21) =381a(22) =91a(23) =178481a(24) =42799a(25) =5a(27) =19065a(28) =4599a(31) =1a(32) =63