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 A204102 #11 Mar 03 2018 05:35:22 %S A204102 2304,31104,419904,5738688,78428736,1073134656,14683622976, %T A204102 200937920832,2749733365824,37629117912384,514941023905344, %U A204102 7046791236157248,96432920316542016,1319651562497299776,18058980695442371136 %N A204102 Number of (n+1) X 5 0..2 arrays with column and row pair sums b(i,j)=a(i,j)+a(i,j-1) and c(i,j)=a(i,j)+a(i-1,j) such that b(i,j)*b(i-1,j)-c(i,j)*c(i,j-1) is nonzero. %C A204102 Also 0..2 arrays with no 2 X 2 subblock having equal diagonal elements or equal antidiagonal elements. %H A204102 R. H. Hardin, <a href="/A204102/b204102.txt">Table of n, a(n) for n = 1..210</a> %F A204102 Empirical: a(n) = 15*a(n-1) - 270*a(n-3) + 324*a(n-4). %F A204102 Empirical g.f.: 576*x*(4 - 6*x - 81*x^2 + 108*x^3) / ((1 - 15*x + 18*x^2)*(1 - 18*x^2)). - _Colin Barker_, Mar 03 2018 %e A204102 Some solutions for n=5: %e A204102 0 2 0 1 2 2 2 1 2 0 2 2 0 0 2 2 0 0 0 2 %e A204102 0 1 0 1 0 1 0 1 2 0 1 1 1 1 2 2 1 1 1 1 %e A204102 2 1 2 2 0 1 2 1 2 0 2 2 0 0 0 2 0 2 2 2 %e A204102 2 0 0 1 1 1 2 1 2 1 1 1 1 1 2 2 0 1 0 1 %e A204102 1 1 2 2 0 1 0 0 2 1 2 2 2 0 2 1 0 1 2 1 %e A204102 0 0 0 1 0 2 2 1 2 1 0 0 1 0 1 1 2 1 2 0 %K A204102 nonn %O A204102 1,1 %A A204102 _R. H. Hardin_, Jan 10 2012