Number of 6-bead necklaces labeled with numbers -n..n not allowing reversal, with sum zero.

Terms

a(0) =26a(1) =297a(2) =1564a(3) =5457a(4) =14838a(5) =34153a(6) =69784a(7) =130401a(8) =227314a(9) =374825a(10) =590580a(11) =895921a(12) =1316238a(13) =1881321a(14) =2625712a(15) =3589057a(16) =4816458a(17) =6358825a(18) =8273228a(19) =10623249a(20) =13479334a(21) =16919145a(22) =21027912a(23) =25898785a(24) =31633186a(25) =38341161a(26) =46141732a(27) =55163249