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A211334 Number of (n+1)X(n+1) -5..5 symmetric matrices with every 2X2 subblock having sum zero and three or four distinct values 1
46, 194, 802, 3322, 13754, 57170, 238650, 1001306, 4222530, 17893954, 76173162, 325583338, 1396612370, 6009460210, 25926690010, 112107619226, 485673993154, 2107375609954, 9156123643082, 39825088001994, 173378643531634 (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) = 8*a(n-1) -114*a(n-3) +81*a(n-4) +646*a(n-5) -276*a(n-6) -1588*a(n-7) -180*a(n-8) +672*a(n-9) -144*a(n-10)

EXAMPLE

Some solutions for n=3

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

.-2..5.-1..0....0.-1.-2.-3....0.-5..2.-1....2..1.-2.-1...-1..0..1..0

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

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

CROSSREFS

Sequence in context: A251460 A235767 A192850 * A160334 A235550 A083358

Adjacent sequences:  A211331 A211332 A211333 * A211335 A211336 A211337

KEYWORD

nonn

AUTHOR

R. H. Hardin Apr 07 2012

STATUS

approved

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Last modified October 15 04:33 EDT 2019. Contains 328026 sequences. (Running on oeis4.)