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A211468 Number of (n+1)X(n+1) -8..8 symmetric matrices with every 2X2 subblock having sum zero and one or three distinct values 1
121, 277, 565, 1101, 2135, 4047, 7739, 14661, 28031, 53463, 102733, 197579, 382143, 740723, 1441747, 2813157, 5505551, 10799509, 21229339, 41813647, 82481877, 162964213, 322323737, 638333051, 1265124641, 2509927951, 4982252633 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Symmetry and 2X2 block sums zero implies that the diagonal x(i,i) are equal modulo 2 and x(i,j)=(x(i,i)+x(j,j))/2*(-1)^(i-j)

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..210

FORMULA

Empirical: a(n) = 3*a(n-1) +13*a(n-2) -43*a(n-3) -68*a(n-4) +255*a(n-5) +185*a(n-6) -810*a(n-7) -289*a(n-8) +1487*a(n-9) +292*a(n-10) -1577*a(n-11) -242*a(n-12) +895*a(n-13) +170*a(n-14) -210*a(n-15) -60*a(n-16)

EXAMPLE

Some solutions for n=3

.-1..3.-1..3...-8..0.-4..8...-4.-2.-2.-2...-3..5.-3..5....8.-6..1.-6

..3.-5..3.-5....0..8.-4..0...-2..8.-4..8....5.-7..5.-7...-6..4..1..4

.-1..3.-1..3...-4.-4..0..4...-2.-4..0.-4...-3..5.-3..5....1..1.-6..1

..3.-5..3.-5....8..0..4.-8...-2..8.-4..8....5.-7..5.-7...-6..4..1..4

CROSSREFS

Sequence in context: A088285 A218172 A083749 * A023696 A038467 A106562

Adjacent sequences:  A211465 A211466 A211467 * A211469 A211470 A211471

KEYWORD

nonn

AUTHOR

R. H. Hardin Apr 12 2012

STATUS

approved

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Last modified November 22 06:15 EST 2019. Contains 329389 sequences. (Running on oeis4.)