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 A211446 Number of (n+1) X (n+1) -7..7 symmetric matrices with every 2 X 2 subblock having sum zero and three or four distinct values. 1
 90, 548, 3296, 19844, 119260, 716592, 4303756, 25835124, 154970728, 928644692, 5557654436, 33210094112, 198105342332, 1179507539876, 7008630194584, 41558569591508, 245903742193060, 1451916609628912, 8554514693602716 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Symmetry and 2 X 2 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..69 EXAMPLE Some solutions for n=3 ..4.-2..3.-4...-1.-3..0..3...-4.-1.-1.-1....0..2.-1.-2...-5..3..0..6 .-2..0.-1..2...-3..7.-4..1...-1..6.-4..6....2.-4..3..0....3.-1.-2.-4 ..3.-1..2.-3....0.-4..1..2...-1.-4..2.-4...-1..3.-2.-1....0.-2..5..1 .-4..2.-3..4....3..1..2.-5...-1..6.-4..6...-2..0.-1..4....6.-4..1.-7 CROSSREFS Sequence in context: A233638 A289792 A156738 * A203787 A203780 A295982 Adjacent sequences: A211443 A211444 A211445 * A211447 A211448 A211449 KEYWORD nonn AUTHOR R. H. Hardin Apr 11 2012 STATUS approved

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Last modified March 25 15:48 EDT 2023. Contains 361528 sequences. (Running on oeis4.)