1,2

Rotations and reflections are allowed, I believe. I have verified the first three entries by hand. The terms 255 and 2874 were taken from the Vicher web page. - N. J. A. Sloane (njas(AT)research.att.com).

Rotations and reflections are not counted. In the bottom half of page 2 of his Rough sketches ... link njas has mistakenly duplicated the third figure in the first column (middle figure in the second column is 180deg rotation), and omitted the stack of three placed horizontally with the middle piece shifted one unit to the right. The count of seven in that group remains correct. [From Owen Whitby (whitbyo(AT)acm.org), Nov 18 2009]

N. J. A. Sloane, Rough sketches illustrating first three terms

M. Vicher, Polyforms

Index entries for sequences related to dominoes

Cf. A121194.

Sequence in context: A052577 A052880 A090357 this_sequence A006056 A098620 A002465

Adjacent sequences: A056783 A056784 A056785 this_sequence A056787 A056788 A056789

nonn,nice,more,new

James A. Sellers (sellersj(AT)math.psu.edu), Aug 28 2000

Edited by N. J. A. Sloane (njas(AT)research.att.com), Aug 17 2006

a(6) and a(7) from Owen Whitby (whitbyo(AT)acm.org), Nov 18 2009