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A140417 Half the number of n X n symmetric binary matrices with each 1 adjacent to some 0 horizontally (and vertically) and each 0 adjacent to some 1 horizontally (and vertically). 0
1, 1, 4, 13, 77, 556, 5859, 83423, 1659982, 45479269, 1727097809, 90646136576, 6583459833641, 661303481127357, 91895146207819652, 17663776192483786871 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,3

LINKS

Table of n, a(n) for n=2..17.

CROSSREFS

Sequence in context: A012075 A197942 A337286 * A301396 A221512 A061143

Adjacent sequences:  A140414 A140415 A140416 * A140418 A140419 A140420

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jun 17 2008

STATUS

approved

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Last modified January 27 23:41 EST 2022. Contains 350654 sequences. (Running on oeis4.)