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A211814 Number of (n+1)X(n+1) -10..10 symmetric matrices with every 2X2 subblock having sum zero and three distinct values 1
188, 414, 812, 1510, 2778, 5014, 9064, 16350, 29566, 53808, 98098, 180732, 333300, 622046, 1161392, 2193998, 4144530, 7912796, 15101998, 29086670, 55991176, 108595704, 210489002, 410470320, 799923628, 1566429434, 3065502158 (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) = 6*a(n-1) +2*a(n-2) -77*a(n-3) +93*a(n-4) +372*a(n-5) -775*a(n-6) -766*a(n-7) +2711*a(n-8) +230*a(n-9) -4967*a(n-10) +1748*a(n-11) +4882*a(n-12) -3055*a(n-13) -2382*a(n-14) +2083*a(n-15) +433*a(n-16) -619*a(n-17) +28*a(n-18) +66*a(n-19) -12*a(n-20)

EXAMPLE

Some solutions for n=3

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

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

.-4..3.-2..3...-4..1.-4..7...-1..0.-2..0...-7..4.-7..4...-6..8-10..8

..5.-4..3.-4....7.-4..7-10...-1..2..0..2....4.-1..4.-1....4.-6..8.-6

CROSSREFS

Sequence in context: A260836 A304279 A099945 * A335592 A233786 A233961

Adjacent sequences:  A211811 A211812 A211813 * A211815 A211816 A211817

KEYWORD

nonn

AUTHOR

R. H. Hardin Apr 21 2012

STATUS

approved

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Last modified September 17 06:16 EDT 2021. Contains 347478 sequences. (Running on oeis4.)