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A203935 Number of lattice 2n-gons with edges on distinct lines. 0
1, 4, 26, 240, 2918, 44424, 816730, 17652320 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,2

COMMENTS

a(n) is the number of self-avoiding polygons on the nXn square lattice having 2n edges (arbitrary perimeter) with an edge on each of the n distinct horizontal and n distinct vertical lines in the lattice.

LINKS

Table of n, a(n) for n=2..9.

StackExchange, Number of cycles in a grid such that each cycle traverse all the lines

EXAMPLE

a(4)=26: 4 symmetries of the Z pentomino; 4 rotations of the step (123 bargraph) hexomino; 8 symmetries of each of the 132 and 213 bargraph hexominoes; and 2 rotations of the heptomino that consists of a 3x3 square with opposite corner cells removed.

CROSSREFS

Sequence in context: A209923 A115416 A052577 * A210912 A210913 A210914

Adjacent sequences:  A203932 A203933 A203934 * A203936 A203937 A203938

KEYWORD

nonn

AUTHOR

David Bevan, Jan 08 2012

EXTENSIONS

a(8) and a(9) from Francisco Mota, Jun 06 2013

STATUS

approved

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Last modified November 28 13:03 EST 2014. Contains 250359 sequences.