Number of 5-bead necklaces labeled with numbers -n..n not allowing reversal, with sum zero.

Terms

a(0) =11a(1) =77a(2) =291a(3) =791a(4) =1761a(5) =3431a(6) =6077a(7) =10021a(8) =15631a(9) =23321a(10) =33551a(11) =46827a(12) =63701a(13) =84771a(14) =110681a(15) =142121a(16) =179827a(17) =224581a(18) =277211a(19) =338591a(20) =409641a(21) =491327a(22) =584661a(23) =690701a(24) =810551a(25) =945361a(26) =1096327a(27) =1264691a(28) =1451741a(29) =1658811