Number of tilings of a 4 X 2n rectangle with L tetrominoes.

Terms

a(0) =1a(1) =2a(2) =10a(3) =42a(4) =182a(5) =790a(6) =3432a(7) =14914a(8) =64814a(9) =281680a(10) =1224182a(11) =5320310a(12) =23122148a(13) =100489226a(14) =436727814a(15) =1898026232a(16) =8248853134a(17) =35849651070a(18) =155803171860a(19) =677123141810