Number of 2 X 2 symmetric matrices over Z(n) having nonzero determinant.

Terms

a(0) =0a(1) =4a(2) =18a(3) =44a(4) =100a(5) =180a(6) =294a(7) =432a(8) =630a(9) =900a(10) =1210a(11) =1548a(12) =2028a(13) =2548a(14) =3150a(15) =3744a(16) =4624a(17) =5436a(18) =6498a(19) =7500a(20) =8820a(21) =10164a(22) =11638a(23) =13104a(24) =14900a(25) =16900a(26) =18792a(27) =20972a(28) =23548a(29) =26100