(1/168)*(sigma_7(2n-1)-sigma_1(2n-1)).

Terms

a(0) =0a(1) =13a(2) =465a(3) =4902a(4) =28483a(5) =115995a(6) =373503a(7) =1017498a(8) =2442492a(9) =5320665a(10) =10725680a(11) =20266818a(12) =36330915a(13) =62292490a(14) =102677835a(15) =163765560a(16) =253797216a(17) =382977372a(18) =565070697a(19) =817224746a(20) =1159251630a(21) =1617967923a(22) =2225268903a(23) =3015613812