Number of 4-bead necklaces labeled with numbers -n..n not allowing reversal, with sum zero.

Terms

a(0) =6a(1) =23a(2) =60a(3) =125a(4) =226a(5) =371a(6) =568a(7) =825a(8) =1150a(9) =1551a(10) =2036a(11) =2613a(12) =3290a(13) =4075a(14) =4976a(15) =6001a(16) =7158a(17) =8455a(18) =9900a(19) =11501a(20) =13266a(21) =15203a(22) =17320a(23) =19625a(24) =22126a(25) =24831a(26) =27748a(27) =30885a(28) =34250a(29) =37851