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 A219871 #10 Nov 28 2016 00:38:19 %S A219871 1,4,123,5233,161800,6155230,223026907,8061851335,295743829064, %T A219871 10750194262698,392127322268846,14301080443962397,521186161714401053, %U A219871 19005127884701974465,692863015545590519355,25260000472133325186613,920954865421382858310101 %N A219871 Number of tilings of an 8 X n rectangle using dominoes and straight (3 X 1) trominoes. %H A219871 Alois P. Heinz, <a href="/A219871/b219871.txt">Table of n, a(n) for n = 0..200</a> %e A219871 a(1) = 4, because there are 4 tilings of an 8 X 1 rectangle using dominoes and straight (3 X 1) trominoes: %e A219871 ._. ._. ._. ._. %e A219871 | | | | | | | | %e A219871 | | | | |_| |_| %e A219871 |_| |_| | | | | %e A219871 | | | | | | |_| %e A219871 | | |_| |_| | | %e A219871 |_| | | | | |_| %e A219871 | | | | | | | | %e A219871 |_| |_| |_| |_| %Y A219871 Column k=8 of A219866. %K A219871 nonn %O A219871 0,2 %A A219871 _Alois P. Heinz_, Nov 30 2012