1,1

Fault-free tilings are those where the only straight interface is at the left and right end. Thus a(n) <= A084480(n).

C. Moore, [math/9905012] Some Polyomino Tilings of the Plane

G.f. 2z(1+z)^2(1-z-z^3)/(1-2z-z^3).

Cf. A084478, A084479, A084480, A084477.

Sequence in context: A077626 A095357 A095358 this_sequence A006553 A054273 A127567

Adjacent sequences: A084478 A084479 A084480 this_sequence A084482 A084483 A084484

nonn,easy

Ralf Stephan (ralf(AT)ark.in-berlin.de), May 27 2003