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A211258 Number of (n+1)X(n+1) -6..6 symmetric matrices with every 2X2 subblock having sum zero and three or four distinct values 1
64, 322, 1602, 7994, 39770, 197618, 980042, 4851354, 23971042, 118229026, 582129930, 2861563514, 14044992402, 68835873986, 336921033210, 1647038902058, 8042362627394, 39229027769714, 191167187783274, 930758796100442 (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) = 13*a(n-1) +13*a(n-2) -721*a(n-3) +779*a(n-4) +18689*a(n-5) -25301*a(n-6) -297919*a(n-7) +287578*a(n-8) +3113878*a(n-9) -880464*a(n-10) -20368976*a(n-11) -8788232*a(n-12) +71301440*a(n-13) +72542540*a(n-14) -93705748*a(n-15) -122099536*a(n-16) +82149632*a(n-17) +97618464*a(n-18) -62699504*a(n-19) -36898656*a(n-20) +34352128*a(n-21) +226560*a(n-22) -8062208*a(n-23) +3326976*a(n-24) -568320*a(n-25) +36864*a(n-26)

EXAMPLE

Some solutions for n=3

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

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

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

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

CROSSREFS

Sequence in context: A221486 A231942 A221686 * A252080 A017366 A186441

Adjacent sequences:  A211255 A211256 A211257 * A211259 A211260 A211261

KEYWORD

nonn

AUTHOR

R. H. Hardin Apr 06 2012

STATUS

approved

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Last modified October 30 22:57 EDT 2020. Contains 338095 sequences. (Running on oeis4.)