login
This site is supported by donations to The OEIS Foundation.

 

Logo

Annual Appeal: Today, Nov 11 2014, is the 4th anniversary of the launch of the new OEIS web site. 70,000 sequences have been added in these four years, all edited by volunteers. Please make a donation (tax deductible in the US) to help keep the OEIS running.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .

Last modified November 25 15:28 EST 2014. Contains 249997 sequences.