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A191601 Number of n X n symmetric binary matrices with each 1 adjacent to no more than 2 horizontally, vertically or diagonally neighboring 1s 1
2, 7, 41, 428, 7588, 235992, 12750773, 1196790145, 195443817921, 55484180929526, 27388366928551712, 23507551792998353446, 35081808543792928475951, 91032423727427789694636918, 410722028606679785606473590135 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..17

EXAMPLE

Some solutions for n=4

..0..1..1..0....1..0..1..1....1..0..0..0....0..0..0..1....1..0..0..1

..1..1..0..0....0..0..0..0....0..0..0..1....0..0..0..1....0..0..0..0

..1..0..0..0....1..0..1..0....0..0..0..1....0..0..1..0....0..0..0..1

..0..0..0..1....1..0..0..0....0..1..1..1....1..1..0..0....1..0..1..1

CROSSREFS

Sequence in context: A084871 A122942 A159315 * A265772 A109172 A131682

Adjacent sequences:  A191598 A191599 A191600 * A191602 A191603 A191604

KEYWORD

nonn

AUTHOR

R. H. Hardin Jun 08 2011

STATUS

approved

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Last modified January 18 16:27 EST 2020. Contains 331011 sequences. (Running on oeis4.)