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A211260 Number of (n+1)X(n+1) -6..6 symmetric matrices with every 2X2 subblock having sum zero and two, three or four distinct values 1
84, 546, 3552, 23154, 151218, 989484, 6486618, 42598386, 280208436, 1845953430, 12177085710, 80422381488, 531677196078, 3517904882982, 23292441203544, 154303014921810, 1022587652767170, 6778549963517052, 44939890595804202 (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..159

FORMULA

Empirical: a(n) = 44*a(n-1) -834*a(n-2) +8822*a(n-3) -56045*a(n-4) +210804*a(n-5) -405935*a(n-6) +122980*a(n-7) +727296*a(n-8) -286484*a(n-9) -957331*a(n-10) -589182*a(n-11) -162870*a(n-12) -21384*a(n-13) -1080*a(n-14)

EXAMPLE

Some solutions for n=3

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

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

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

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

CROSSREFS

Sequence in context: A329935 A233055 A233056 * A233053 A220203 A008429

Adjacent sequences:  A211257 A211258 A211259 * A211261 A211262 A211263

KEYWORD

nonn

AUTHOR

R. H. Hardin Apr 06 2012

STATUS

approved

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Last modified November 27 12:51 EST 2021. Contains 349394 sequences. (Running on oeis4.)