

A056780


Rectangular free polyominoes: number of ncelled polyominoes when the cell is a rectangle.


5



1, 2, 3, 9, 21, 68, 208, 730, 2542, 9287, 34053, 127112, 476849, 1803636, 6851960, 26157362, 100211446, 385239872, 1485232325, 5741327939, 22246061118, 86383655207, 336093789246, 1309999171971, 5114453234510, 19998176771431, 78306018629550, 307022197845116
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OFFSET

1,2


LINKS

Table of n, a(n) for n=1..28.
R. J. Mathar, Illustration of shapes up to 7ominoes
Ed Pegg, Jr., Illustrations of polyforms
M. Vicher, Polyforms
M. Vicher, The 21 5celled rectangular polyominoes
M. Vicher, The 21 5celled rectangular polyominoes
Eric Weisstein's World of Mathematics, Polyrect [From Eric W. Weisstein, Apr 24 2009]
Wikipedia, Polyomino


FORMULA

a(n) = 2*A006749(n) + 2*A006746(n) + A006748(n) + 2*A006747(n) + 2*A056877(n) + A056878(n) + A144553(n) + A142886(n).  Andrew Howroyd, Dec 04 2018


CROSSREFS

Cf. A000105 (cell is square), A151522 (1sided), A001168 (fixed).
Sequence in context: A099607 A077550 A301809 * A141505 A111360 A111238
Adjacent sequences: A056777 A056778 A056779 * A056781 A056782 A056783


KEYWORD

nice,nonn,hard,changed


AUTHOR

James A. Sellers, Aug 28 2000


EXTENSIONS

Edited by N. J. A. Sloane, Apr 25, 2001
Two more terms from Ed Pegg Jr, May 13 2009
a(13)a(18) from Joseph Myers, Nov 15 2010
a(19)a(28) from Andrew Howroyd, Dec 04 2018


STATUS

approved



