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 A251073 #10 Feb 06 2017 18:20:16 %S A251073 1,1,1,19,57,121,783,2861,8133,37160,143419,468816,1876855,7263468, %T A251073 25496863,97187247,372086645,1352780401,5071962134,19220628318, %U A251073 71025008365,265095817718,997839772024,3713274525679,13851695644227,51940567251136,193830054345968 %N A251073 Number of tilings of a 9 X n rectangle using 3n trominoes of shape I. %H A251073 Alois P. Heinz, <a href="/A251073/b251073.txt">Table of n, a(n) for n = 0..1000</a> %H A251073 Alois P. Heinz, <a href="/A251073/a251073.txt">G.f. and Maple program for A251073</a> %H A251073 Wikipedia, <a href="https://en.wikipedia.org/wiki/Tromino">Tromino</a> %F A251073 G.f.: see link above. %p A251073 # see link above. %Y A251073 Column k=3 of A251072. %Y A251073 Cf. A236577. %K A251073 nonn %O A251073 0,4 %A A251073 _Alois P. Heinz_, Nov 29 2014