Number of n X n (-1,1)-circulant matrices with determinant 0.

Terms

a(0) =0a(1) =0a(2) =4a(3) =2a(4) =8a(5) =2a(6) =40a(7) =2a(8) =128a(9) =62a(10) =504a(11) =2a(12) =1768a(13) =2a(14) =6864a(15) =2738a(16) =24192a(17) =2a(18) =107128a(19) =2a(20) =331096a(21) =109334a(22) =1410864a(23) =2a(24) =5880544a(25) =206282a(26) =20801200a(27) =5417630a(28) =73508696a(29) =2