Alternating sum of 9-gonal (or nonagonal) numbers.

Terms

a(0) =0a(1) =-1a(2) =8a(3) =-16a(4) =30a(5) =-45a(6) =66a(7) =-88a(8) =116a(9) =-145a(10) =180a(11) =-216a(12) =258a(13) =-301a(14) =350a(15) =-400a(16) =456a(17) =-513a(18) =576a(19) =-640a(20) =710a(21) =-781a(22) =858a(23) =-936a(24) =1020a(25) =-1105a(26) =1196a(27) =-1288a(28) =1386a(29) =-1485