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 A233290 #18 Feb 07 2017 17:11:56 %S A233290 1,1,11,170,939,8342,80092,614581,5271923,45832761,379419508, %T A233290 3223419241,27438555522,231096250072,1958024834151,16593169804557, %U A233290 140295718998907,1187830239559588,10056816580083721,85104482994177208,720410915948382970,6098207777286812381 %N A233290 Number of tilings of a 6 X n rectangle with 2n trominoes of any shape. %H A233290 Alois P. Heinz, <a href="/A233290/b233290.txt">Table of n, a(n) for n = 0..1000</a> %H A233290 Vaclav Kotesovec, <a href="/A233290/a233290.txt">Recurrence (of order 126) and G.f.</a> %H A233290 Wikipedia, <a href="https://en.wikipedia.org/wiki/Tromino">Tromino</a> %e A233290 a(2) = 11: %e A233290 .___. .___. .___. .___. .___. .___. .___. .___. .___. .___. .___. %e A233290 | | | | ._| |_. | | ._| | | | |_. | | | | |_. | | ._| | ._| |_. | %e A233290 | | | |_| | | |_| |_| | | | | | |_| | | | | |_| |_| | |_| | | |_| %e A233290 |_|_| |___| |___| |___| |_|_| |___| |_|_| |___| |___| | | | | | | %e A233290 | | | | ._| |_. | | | | | ._| | | | |_. | | ._| |_. | | |_| |_| | %e A233290 | | | |_| | | |_| | | | |_| | | | | | |_| |_| | | |_| |_| | | |_| %e A233290 |_|_| |___| |___| |_|_| |___| |_|_| |___| |___| |___| |___| |___|. %Y A233290 Column k=6 of A233320. %Y A233290 Cf. A134438, A215826, A269664. %K A233290 nonn %O A233290 0,3 %A A233290 _Alois P. Heinz_, Dec 06 2013