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 A219974 #7 Dec 07 2012 12:51:16 %S A219974 1,0,7,58,286,3068,29876,214485,1910822,17671945,141365332,1225043571, %T A219974 10871708273,90688536786,781019641877,6800784990468,57716277595775, %U A219974 496096480109463,4284929501626939,36621478929328140,314572431365390797,2707867101849205129 %N A219974 Number of tilings of a 10 X n rectangle using straight (3 X 1) trominoes and 2 X 2 tiles. %e A219974 a(2) = 7, because there are 7 tilings of a 10 X 2 rectangle using straight (3 X 1) trominoes and 2 X 2 tiles: %e A219974 .___. .___. .___. .___. .___. .___. .___. %e A219974 | | | | | | | | | | | | | | | | | %e A219974 |___| |___| |___| | | | |___| | | | | | | %e A219974 | | | | | | | |_|_| | | | |_|_| |_|_| %e A219974 |___| |___| | | | | | | | | | | | | | %e A219974 | | | | | |_|_| |___| |_|_| |___| | | | %e A219974 |___| | | | | | | | | | | | | | |_|_| %e A219974 | | |_|_| |___| |___| | | | | | | | | %e A219974 |___| | | | | | | | | | |_|_| |_|_| |___| %e A219974 | | | | | | | | | | | | | | | | | %e A219974 |___| |_|_| |_|_| |_|_| |___| |___| |___| %Y A219974 Column k=10 of A219967. %K A219974 nonn %O A219974 0,3 %A A219974 _Alois P. Heinz_, Dec 02 2012