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 A273477 #6 Feb 06 2017 12:39:56 %S A273477 1,1,23,1086,13097,261110,5732276,105028302,2057123951,40750196324, %T A273477 789214306848,15416490294168,301533431477968,5881271193704355, %U A273477 114836714153318686,2242611029205195253,43780084385383228801,854790034707804119211,16689735991827528511674 %N A273477 Number of tilings of a 7 X n rectangle using pentominoes of shapes W, U, X and monominoes. %H A273477 Alois P. Heinz, <a href="/A273477/b273477.txt">Table of n, a(n) for n = 0..775</a> %H A273477 Wikipedia, <a href="https://en.wikipedia.org/wiki/Pentomino">Pentomino</a> %Y A273477 Cf. A264765. %K A273477 nonn %O A273477 0,3 %A A273477 _Alois P. Heinz_, May 23 2016