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A056787 Number of incongruental unlabeled undirected trees with n nodes on a square lattice and edges of length 1 or sqrt(2) admitted to the 4 nearest or 4 2nd nearest neighbors. 3
1, 2, 6, 40, 303, 2929 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n)>=A056841(n) since the trees of A056841 are a subset of these here. Edges along diagonals may cross.

LINKS

Table of n, a(n) for n=1..6.

M. Vicher, Polyforms

R. J. Mathar, C++ program

R. J. Mathar, Polyforms (ASCII art)

EXAMPLE

For n=2 we have

o-o

and

..o

./.

o..

as the only a(2)=2 candidates. Trees contributing to n=7 are

o.o-o

|\.\.

o.o-o

...\.

....o

or

o....

|\...

o.o-o

...X.

..o.o

./...

o....

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.

CROSSREFS

See also A056840, A056841.

Sequence in context: A081096 A119692 A098854 * A098852 A120592 A081471

Adjacent sequences:  A056784 A056785 A056786 * A056788 A056789 A056790

KEYWORD

nonn

AUTHOR

James A. Sellers, Aug 28 2000

EXTENSIONS

Edited by R. J. Mathar, Apr 13 2006

STATUS

approved

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Last modified July 24 06:42 EDT 2014. Contains 244876 sequences.