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 A194992 #9 Oct 18 2021 13:41:44 %S A194992 3,6,20,80,576,4608,69632,1114112,34603008,1107296256,69793218560, %T A194992 4466765987840,567347999932416,72620543991349248,18518801667747479552, %U A194992 4740813226943354765312,2422574005712127994626048 %N A194992 Number of lower triangles of an n X n 0..2 array with each element differing from all of its horizontal and vertical neighbors by one. %C A194992 Column 2 of A194998. %H A194992 R. H. Hardin, <a href="/A194992/b194992.txt">Table of n, a(n) for n = 1..89</a> %e A194992 Some solutions for 4 X 4 %e A194992 ..2........1........0........2........0........0........0........0 %e A194992 ..1.0......2.1......1.2......1.0......1.0......1.0......1.0......1.0 %e A194992 ..2.1.2....1.2.1....0.1.0....2.1.2....2.1.0....0.1.0....2.1.0....2.1.0 %e A194992 ..1.0.1.0..2.1.2.1..1.2.1.0..1.2.1.0..1.2.1.2..1.0.1.2..1.2.1.0..1.0.1.2 %Y A194992 Cf. A194998. %K A194992 nonn %O A194992 1,1 %A A194992 _R. H. Hardin_, Sep 07 2011