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A211551 Number of (n+1)X(n+1) -9..9 symmetric matrices with every 2X2 subblock having sum zero and one or three distinct values 1
151, 347, 697, 1351, 2573, 4843, 9101, 17119, 32217, 61049, 115711, 221303, 423135, 816445, 1574315, 3060679, 5945293, 11628771, 22724533, 44657457, 87680827, 172920419, 340748827, 673800359, 1331438461, 2638045435, 5223798103 (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
FORMULA
Empirical: a(n) = 4*a(n-1) +11*a(n-2) -60*a(n-3) -34*a(n-4) +375*a(n-5) -53*a(n-6) -1270*a(n-7) +601*a(n-8) +2541*a(n-9) -1636*a(n-10) -3075*a(n-11) +2204*a(n-12) +2210*a(n-13) -1562*a(n-14) -875*a(n-15) +530*a(n-16) +150*a(n-17) -60*a(n-18)
EXAMPLE
Some solutions for n=3
..8.-2..8.-3....5.-7.-1.-7....5.-1..5.-2...-1..4..4..4....3.-5..3.-5
.-2.-4.-2.-3...-7..9.-1..9...-1.-3.-1.-2....4.-7.-1.-7...-5..7.-5..7
..8.-2..8.-3...-1.-1.-7.-1....5.-1..5.-2....4.-1..9.-1....3.-5..3.-5
.-3.-3.-3.-2...-7..9.-1..9...-2.-2.-2.-1....4.-7.-1.-7...-5..7.-5..7
CROSSREFS
Sequence in context: A031893 A118494 A140022 * A108842 A078858 A217498
KEYWORD
nonn
AUTHOR
R. H. Hardin Apr 15 2012
STATUS
approved

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Last modified May 26 22:32 EDT 2024. Contains 372847 sequences. (Running on oeis4.)