This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A115223 #3 Mar 30 2012 17:22:41
%S A115223 1,36,261,1408,3225,9396,17101,47104,76545,116100,162261,367488,
%T A115223 373321,615636,841725,1638400,1424481,2755620,2482597,4540800,4463361,
%U A115223 5841396,6447981,12294144,11640625,13439556,18954729,24078208,20534697,30302100
%N A115223 Number of 3 X 3 symmetric matrices over Z(n) having determinant 0.
%F A115223 a(n)=n^6-A115225(n). For prime n, a(n)=(n^3+n-1)n^2.
%t A115223 Table[cnt=0; Do[m={{a, b, c}, {b, d, e}, {c, e, f}}; If[Det[m, Modulus->n]==0, cnt++ ], {a, 0, n-1}, {b, 0, n-1}, {c, 0, n-1}, {d, 0, n-1}, {e, 0, n-1}, {f, 0, n-1}]; cnt, {n, 2, 20}]
%Y A115223 Cf. A115221 (number of 3 X 3 matrices over Z(n) having determinant 0).
%K A115223 mult,nonn
%O A115223 1,2
%A A115223 _T. D. Noe_, Jan 16 2006