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 A194993 #8 Jul 22 2025 12:39:21 %S A194993 4,10,42,248,2290,31042,641376,19753266,918924546,64065187024, %T A194993 6724991990090,1059952700132050,251257954485037072, %U A194993 89488725743024413554,47916300899545924260762,38558096411377540692559456 %N A194993 Number of lower triangles of an n X n 0..3 array with each element differing from all of its horizontal and vertical neighbors by one. %C A194993 Column 3 of A194998 %H A194993 R. H. Hardin, <a href="/A194993/b194993.txt">Table of n, a(n) for n = 1..32</a> %e A194993 Some solutions for 4X4 %e A194993 ..1........3........2........3........1........2........1........3 %e A194993 ..2.3......2.1......1.2......2.1......0.1......3.2......2.1......2.3 %e A194993 ..1.2.3....1.2.3....2.1.2....3.2.3....1.2.3....2.1.2....1.2.1....3.2.1 %e A194993 ..0.1.2.3..0.1.2.3..3.2.3.2..2.3.2.3..2.3.2.1..3.2.1.2..2.1.2.3..2.1.0.1 %K A194993 nonn %O A194993 1,1 %A A194993 _R. H. Hardin_ Sep 07 2011