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A211332 Number of (n+1)X(n+1) -5..5 symmetric matrices with every 2X2 subblock having sum zero and two or three distinct values 1
60, 144, 312, 630, 1266, 2474, 4864, 9466, 18544, 36252, 71260, 140314, 277456, 550506, 1095678, 2189478, 4384860, 8817146, 17756308, 35895256, 72635652, 147493822, 299688524, 610819886, 1245448294, 2546376998, 5207461228 (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) = 5*a(n-1) +8*a(n-2) -75*a(n-3) +16*a(n-4) +467*a(n-5) -412*a(n-6) -1551*a(n-7) +2039*a(n-8) +2909*a(n-9) -5118*a(n-10) -2897*a(n-11) +7385*a(n-12) +976*a(n-13) -6197*a(n-14) +720*a(n-15) +2888*a(n-16) -760*a(n-17) -674*a(n-18) +236*a(n-19) +60*a(n-20) -24*a(n-21)

EXAMPLE

Some solutions for n=3

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

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

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

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

CROSSREFS

Sequence in context: A043478 A044311 A044692 * A039497 A218243 A218392

Adjacent sequences:  A211329 A211330 A211331 * A211333 A211334 A211335

KEYWORD

nonn

AUTHOR

R. H. Hardin Apr 07 2012

STATUS

approved

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Last modified October 23 17:19 EDT 2019. Contains 328373 sequences. (Running on oeis4.)