

A089243


Number of partitions into strokes of the edges of a star graph with n edges.


2




OFFSET

1,3


COMMENTS

Two arrangements are considered the same if one is a rotation or reflection of the other.
A "stroke" is defined as follows. If the following conditions are satisfied then the partition to directed paths on a directed graph is called "a partition to strokes on a directed graph". And all directed paths in the partition are called "strokes". C.1. Two different directed paths in a partition do not have the same edges. C.2. A union of two different paths in a partition does not become a directed path. In other word, a "stroke" is a locally maximal path on a directed graph.
This sequence has its origin in the strokes made when writing Japanese Kanji.


LINKS

Table of n, a(n) for n=1..7.


EXAMPLE

n=3: this the Y graph. Call the center node "0" and the terminal nodes "1", "2", "3". Four partitions exist as follows:
{1>0>2, 0>3}
{1>0>2, 3>0}
{1>0, 2>0, 3>0}
{0>1, 0>2, 0>3}
So a(3)=4.


CROSSREFS

Sequence in context: A116868 A049976 A032789 * A299123 A245455 A296265
Adjacent sequences: A089240 A089241 A089242 * A089244 A089245 A089246


KEYWORD

nonn


AUTHOR

Yasutoshi Kohmoto


STATUS

approved



