Number of cyclic Steiner triple systems of order 2n+1.

Terms

a(0) =1a(1) =1a(2) =0a(3) =1a(4) =0a(5) =0a(6) =1a(7) =2a(8) =0a(9) =4a(10) =7a(11) =0a(12) =12a(13) =8a(14) =0a(15) =80a(16) =84a(17) =0a(18) =820a(19) =798a(20) =0a(21) =9508a(22) =11616a(23) =0a(24) =157340a(25) =139828a(26) =0a(27) =3027456a(28) =2353310