%I
%S 1,0,1,2,3,28,267,2744,66653,2766100,141365332,13305552648,
%T 2149055591278
%N Number of tilings of an n X n square using straight (3 X 1) trominoes and 2 X 2 tiles.
%e a(4) = 3, because there are 3 tilings of a 4 X 4 square using straight (3 X 1) trominoes and 2 X 2 tiles:
%e ._._____. ._____._. ._._._._.
%e  _____ _____   .  . 
%e   .     .   ______
%e ____   ____  .  . 
%e ______ ______ ______ .
%Y Main diagonal of A219967.
%Y Cf. A233807.
%K nonn,more
%O 0,4
%A _Alois P. Heinz_, Dec 02 2012
%E a(12) from _Alois P. Heinz_, Sep 24 2014
