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a(n)>=A056841(n) since the trees of A056841 are a subset of these here. Edges along diagonals may cross.
Table of n, a(n) for n=1..6.
M. Vicher, Polyforms
R. J. Mathar, C++ program
R. J. Mathar, Polyforms (ASCII art)
For n=2 we have
as the only a(2)=2 candidates. Trees contributing to n=7 are
where dashes are edges in E, NE, N, NW, W, SW, S or SE direction that connect nodes marked 'o' horizontally, vertically or along diagonals, and X's are crossing diagonal edges.
See also A056840, A056841.
Sequence in context: A119692 A264152 A098854 * A098852 A274482 A274277
Adjacent sequences: A056784 A056785 A056786 * A056788 A056789 A056790
James A. Sellers, Aug 28 2000
Edited by R. J. Mathar, Apr 13 2006