Number of 3 X 3 symmetric matrices over Z(n) having nonzero determinant.

Terms

a(0) =0a(1) =28a(2) =468a(3) =2688a(4) =12400a(5) =37260a(6) =100548a(7) =215040a(8) =454896a(9) =883900a(10) =1609300a(11) =2618496a(12) =4453488a(13) =6913900a(14) =10548900a(15) =15138816a(16) =22713088a(17) =31256604a(18) =44563284a(19) =59459200a(20) =81302760a(21) =107538508a(22) =141587908a(23) =178808832a(24) =232500000a(25) =295476220a(26) =368465760