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A211818 Number of (n+1)X(n+1) -10..10 symmetric matrices with every 2X2 subblock having sum zero and three or four distinct values 0
188, 1702, 15334, 138130, 1242978, 11177174, 100431854, 901725738, 8089235074, 72498715894, 649077462926, 5804421919322, 51840849262274, 462375098375406, 4118031964300046, 36620792527293818 (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

Table of n, a(n) for n=1..16.

EXAMPLE

Some solutions for n=3

..6..2..5..2..-10..9-10..3....9.-6..2.-5....9.-2..4.-2...-8..1.-3.-1

..2-10..3-10....9.-8..9.-2...-6..3..1..2...-2.-5..3.-5....1..6.-4..8

..5..3..4..3..-10..9-10..3....2..1.-5..2....4..3.-1..3...-3.-4..2.-6

..2-10..3-10....3.-2..3..4...-5..2..2..1...-2.-5..3.-5...-1..8.-6.10

CROSSREFS

Sequence in context: A073586 A064115 A185241 * A204071 A089273 A035832

Adjacent sequences:  A211815 A211816 A211817 * A211819 A211820 A211821

KEYWORD

nonn

AUTHOR

R. H. Hardin Apr 21 2012

STATUS

approved

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Last modified July 31 10:51 EDT 2021. Contains 346373 sequences. (Running on oeis4.)