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 A211843 #6 Jun 02 2025 07:49:24 %S A211843 1,7,35,147,561,2013,6936,23244,76434,248158,799178,2561866,8197109, %T A211843 26236283,84147409,270824081,875656255,2846900003,9313478684, %U A211843 30675454100,101762486216,340118043072,1145518666868,3888262008004,13301838021901 %N A211843 Number of nonnegative integer arrays of length n+5 with new values 0 upwards introduced in order, no three adjacent elements all unequal, and containing the value 3. %C A211843 Column 2 of A211849 %H A211843 R. H. Hardin, <a href="/A211843/b211843.txt">Table of n, a(n) for n = 1..210</a> %e A211843 Some solutions for n=3 %e A211843 ..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0 %e A211843 ..1....1....1....1....1....1....1....0....1....0....1....1....1....1....0....1 %e A211843 ..0....1....1....1....1....1....1....1....1....0....1....1....1....1....1....1 %e A211843 ..0....2....2....1....2....2....2....1....2....1....1....2....1....2....1....2 %e A211843 ..2....1....2....2....2....2....2....1....2....1....2....2....1....2....2....1 %e A211843 ..0....2....2....2....3....3....3....2....3....2....1....3....2....3....2....1 %e A211843 ..0....2....2....3....3....2....3....2....2....2....1....3....2....3....3....3 %e A211843 ..3....3....3....3....1....3....3....3....2....3....3....2....3....0....2....1 %K A211843 nonn %O A211843 1,2 %A A211843 _R. H. Hardin_ Apr 22 2012