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A211816 Number of (n+1)X(n+1) -10..10 symmetric matrices with every 2X2 subblock having sum zero and two or three distinct values 1
220, 602, 1368, 2942, 6088, 12442, 24924, 50194, 99390, 199570, 394162, 793028, 1569220, 3170790, 6300354, 12799142, 25565534, 52235044, 104925530, 215604840, 435513812, 899750556, 1827061522, 3793414420, 7740115362, 16142443314 (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) +16*a(n-2) -160*a(n-3) -15*a(n-4) +1883*a(n-5) -1614*a(n-6) -12827*a(n-7) +18643*a(n-8) +55534*a(n-9) -110733*a(n-10) -156457*a(n-11) +420605*a(n-12) +273571*a(n-13) -1096609*a(n-14) -220702*a(n-15) +2018897*a(n-16) -191679*a(n-17) -2645653*a(n-18) +814093*a(n-19) +2453538*a(n-20) -1164914*a(n-21) -1580007*a(n-22) +985631*a(n-23) +680255*a(n-24) -535843*a(n-25) -180672*a(n-26) +188098*a(n-27) +23218*a(n-28) -41026*a(n-29) +676*a(n-30) +5032*a(n-31) -568*a(n-32) -264*a(n-33) +48*a(n-34)

EXAMPLE

Some solutions for n=3

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

..3.-5..3.-1...-2.-2..0.-2...-3..9.-3..6....2.-3..2.-3....1.-4..2.-4

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

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

CROSSREFS

Sequence in context: A260203 A184543 A234558 * A135807 A258545 A257361

Adjacent sequences:  A211813 A211814 A211815 * A211817 A211818 A211819

KEYWORD

nonn

AUTHOR

R. H. Hardin Apr 21 2012

STATUS

approved

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Last modified October 26 02:14 EDT 2021. Contains 348256 sequences. (Running on oeis4.)