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A211467 Number of (n+1)X(n+1) -8..8 symmetric matrices with every 2X2 subblock having sum zero and three distinct values 1
120, 260, 508, 940, 1734, 3126, 5690, 10276, 18758, 34230, 63068, 116594, 217310, 407026, 767450, 1454628, 2771646, 5306940, 10202586, 19697838, 38146332, 74135060, 144403432, 282088738, 551970304, 1082582606, 2125859552, 4182450010 (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) = 4*a(n-1) +9*a(n-2) -52*a(n-3) -16*a(n-4) +271*a(n-5) -86*a(n-6) -724*a(n-7) +435*a(n-8) +1052*a(n-9) -760*a(n-10) -817*a(n-11) +575*a(n-12) +320*a(n-13) -150*a(n-14) -60*a(n-15)

EXAMPLE

Some solutions for n=3

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

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

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

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

CROSSREFS

Sequence in context: A028976 A158130 A070856 * A257712 A250607 A076579

Adjacent sequences:  A211464 A211465 A211466 * A211468 A211469 A211470

KEYWORD

nonn

AUTHOR

R. H. Hardin Apr 12 2012

STATUS

approved

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Last modified May 21 03:13 EDT 2022. Contains 353886 sequences. (Running on oeis4.)