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 A242542 #7 Jul 23 2025 11:16:59 %S A242542 6,32,150,690,3311,16968,93103,544920,3386262,22243902,153850981, %T A242542 1116625523,8478969009,67185160511,554235206898,4750165417926, %U A242542 42219358673456,388485398829204,3695187060252009,36282147267628868 %N A242542 Number of length n+3 0..n arrays with no four elements in a row with pattern aabb (possibly a=b) and new values 0..n introduced in 0..n order. %C A242542 Diagonal of A242549 %H A242542 R. H. Hardin, <a href="/A242542/b242542.txt">Table of n, a(n) for n = 1..132</a> %e A242542 Some solutions for n=4 %e A242542 ..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0 %e A242542 ..1....0....1....0....1....1....1....1....1....1....1....1....1....1....1....1 %e A242542 ..2....1....0....1....0....2....2....2....1....2....2....1....1....0....1....2 %e A242542 ..0....2....2....2....2....0....2....1....0....1....0....2....1....2....0....1 %e A242542 ..1....2....2....1....0....3....1....0....2....3....2....1....0....1....1....2 %e A242542 ..0....1....1....3....3....1....3....2....1....3....3....1....1....0....0....1 %e A242542 ..3....2....0....2....0....3....4....3....3....2....2....2....1....0....2....3 %K A242542 nonn %O A242542 1,1 %A A242542 _R. H. Hardin_, May 17 2014