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A191006 Number of n X n symmetric binary matrices with each 1 adjacent to exactly 1 diagonally neighboring 1 1
1, 2, 6, 24, 144, 1296, 16848, 320112, 8963136, 367488576, 22049314560, 1940339681280, 250303818885120, 47307421769287680, 13104155830092687360, 5320287267017631068160, 3165570923875490485555200 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..49

FORMULA

Empirical: a(n) = a(n-1) * A000930(n+1), so from the formula there

Empirical: a(n) = product(sum(binomial(k+1-2*i,i), i=0..floor((k+1)/3)), k=1..n)

EXAMPLE

Some solutions for n=5

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

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

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

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

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

CROSSREFS

a(n+1)/a(n) is A000930(n+2)

Sequence in context: A205182 A326780 A258325 * A082471 A275594 A013010

Adjacent sequences:  A191003 A191004 A191005 * A191007 A191008 A191009

KEYWORD

nonn

AUTHOR

R. H. Hardin Jun 16 2011

STATUS

approved

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Last modified June 20 14:54 EDT 2021. Contains 345165 sequences. (Running on oeis4.)