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A056841
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Number of diagonal polyominoes with n cells.
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3
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OFFSET
| 1,3
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COMMENTS
| Apparently the cells are circular blobs which must be connected diagonally and the polyominoes can be rotated by 90 degrees and turned over.
Also the number of essentially different (i.e. not related by reflections, translations or rotations) diagrams consisting of n nodes in Z^2 and n-1 horizontal or vertical edges of length 1 between pairs of nodes such that the resulting graph is connected (hence a tree). - Paul Boddington (psb(AT)maths.warwick.ac.uk), Jul 27 2004
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LINKS
| M. Vicher, Polyforms
M. Vicher, The 15 5-celled diagonal polyominoes
M. Vicher, The 15 5-celled diagonal polyominoes
R. J. Mathar, Table of all such polyominoes with n <= 10 cells (gzipped)
R. J. Mathar, C++ program
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EXAMPLE
| The polyominoes with 1, 2, 3 and 4 cells are
O..O...O...O.O..O....O....O.....O....O.O
....O...O...O....O....O....O...O.O..O.O.
.........O........O....O..O.O...O.......
...................O..O.................
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CROSSREFS
| See also A056840, A056787.
Sequence in context: A125280 A022493 A006966 * A107112 A193318 A171450
Adjacent sequences: A056838 A056839 A056840 * A056842 A056843 A056844
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KEYWORD
| nonn,nice
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AUTHOR
| James A. Sellers (sellersj(AT)math.psu.edu), Aug 28 2000
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EXTENSIONS
| Description revised by N. J. A. Sloane (njas(AT)research.att.com), Jun 21 2001
a(10) from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 10 2006
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