A191506 - OEIS

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A191506

Number of n X n symmetric binary matrices with each 1 adjacent to no more than 1 horizontally or vertically neighboring 1

2, 5, 25, 195, 2475, 53324, 1872113, 109037035, 10508450377, 1672058437225, 440124911303718, 191498508664286039, 137739615464486164780, 163796811382099494131871, 322006666961136384120723488

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Ron Hardin, Table of n, a(n) for n = 1..26

EXAMPLE

Some solutions for n=4

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

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

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

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

CROSSREFS