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 A069449 #9 Apr 07 2021 18:41:16 %S A069449 7,269,5799,95783,1389619,18772467,243194821,3070812013 %N A069449 Half the number of 4 X n binary arrays with no path of adjacent 1's or adjacent 0's from top to bottom or side to side. %Y A069449 Cf. 2 X n A000225, vertical path of 1 A069361-A069395, vertical paths of 0+1 A069396-A069416, vertical path of 1 not 0 A069417-A069428, no vertical paths A069429-A069447, no horizontal or vertical paths A069448-A069452. %K A069449 nonn %O A069449 2,1 %A A069449 _R. H. Hardin_, Mar 22 2002