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A034010 Number of 2n-step self avoiding closed walks on square grid, restricted to a quadrant and passing through origin. 2
0, 1, 2, 6, 20, 74, 300, 1302, 5944, 28266, 139010, 703102, 3641956, 19255106, 103630920, 566522778, 3140130354, 17620845976, 99977635264, 572935630884, 3313078283974 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..21.

B. Hayes, How to avoid yourself, American Scientist, Vol. 86, Number 4, Jul-August 1998. p. 314-319.

EXAMPLE

When the number of steps is 8, one of the six closed paths is

0___.

| ._|

|_|

CROSSREFS

A subset of the polyominoes with perimeter 2n (A006725), also a subset of A002931. Cf. A000105, A038373.

Sequence in context: A188144 A245734 A150158 * A135588 A318402 A293492

Adjacent sequences:  A034007 A034008 A034009 * A034011 A034012 A034013

KEYWORD

nonn,hard,walk

AUTHOR

Felice Russo

EXTENSIONS

Corrected and extended by David W. Wilson

a(16)-a(18) from Alex Chernov, Jan 22 2012

a(19)-a(21) from Bert Dobbelaere, Jan 06 2019

STATUS

approved

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Last modified November 19 16:35 EST 2019. Contains 329321 sequences. (Running on oeis4.)