A025234 An L-tile is a 2 X 2 square with the upper 1 X 1 subsquare removed; no rotations are allowed. a(n) = number of tilings of a 4 X n rectangle using tiles that are either 1 X 1 squares or L-tiles.

1, 0, 4, 8, 28, 83, 255, 778, 2377, 7259, 22173, 67721, 206844, 631764, 1929609, 5893632, 18001012, 54980764, 167928588, 512906847, 1566579211, 4784826786, 14614369465, 44636891651, 136335139273, 416410496177, 1271848932360, 3884627600872, 11864877355729

Offset: 0

Author

N. J. A. Sloane, Mar 07 2003

Keywords

• nonn
• easy

Links

• E. Deutsch, Counting tilings with L-tiles and squares, Problem 10877, Amer. Math. Monthly, 110 (March 2003), 245-246.
• Index entries for linear recurrences with constant coefficients, signature (1,5,4,0,-1).

Crossrefs

Cf. A002478.

Formula

G.f.: (1-x-x^2)/(1-x-5*x^2-4*x^3+x^5).