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 A219872 #8 Dec 07 2012 12:41:45 %S A219872 1,5,249,17395,862953,53074167,3105936858,181382499259,10750194262698, %T A219872 631206895803116,37197513508819191,2191568660367709311, %U A219872 129026759279686110418,7600920859497795763717,447657086066162084823497,26365510156948695071183306 %N A219872 Number of tilings of a 9 X n rectangle using dominoes and straight (3 X 1) trominoes. %H A219872 Alois P. Heinz, <a href="/A219872/b219872.txt">Table of n, a(n) for n = 0..75</a> %e A219872 a(1) = 5, because there are 5 tilings of a 9 X 1 rectangle using dominoes and straight (3 X 1) trominoes: %e A219872 ._. ._. ._. ._. ._. %e A219872 | | | | | | | | | | %e A219872 | | |_| |_| |_| | | %e A219872 |_| | | | | | | |_| %e A219872 | | |_| |_| | | | | %e A219872 | | | | | | |_| |_| %e A219872 |_| |_| | | | | | | %e A219872 | | | | |_| |_| |_| %e A219872 | | | | | | | | | | %e A219872 |_| |_| |_| |_| |_| %Y A219872 Column k=9 of A219866. %K A219872 nonn %O A219872 0,2 %A A219872 _Alois P. Heinz_, Nov 30 2012