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 A056841 Number of diagonal polyominoes with n cells. 4
 1, 1, 2, 5, 15, 54, 212, 908, 4011, 18260, 84320 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 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, Jul 27 2004 LINKS R. J. Mathar, Table of all such polyominoes with n <= 10 cells (gzipped) R. J. Mathar, C++ program Douglas A. Torrance, Enumeration of planar Tangles, arXiv:1906.01541 [math.CO], 2019-2020. See Table 4.1 (C). M. Vicher, Polyforms M. Vicher, The 15 5-celled diagonal polyominoes M. Vicher, The 15 5-celled diagonal polyominoes 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................. CROSSREFS See also A056840, A056787. Sequence in context: A006966 A336020 A277175 * A185040 A208237 A321958 Adjacent sequences:  A056838 A056839 A056840 * A056842 A056843 A056844 KEYWORD nonn,nice,more AUTHOR James A. Sellers, Aug 28 2000 EXTENSIONS Description revised by N. J. A. Sloane, Jun 21 2001 a(10) from R. J. Mathar, Apr 10 2006 a(11) from Douglas A. Torrance, Mar 06 2020 STATUS approved

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Last modified April 21 19:16 EDT 2021. Contains 343156 sequences. (Running on oeis4.)