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A211477 Number of -1..1 arrays x(i) of n+1 elements i=1..n+1 with x(i)+x(j), x(i+1)+x(j+1), -(x(i)+x(j+1)), and -(x(i+1)+x(j)) having two or three distinct values for every i<=n and j<=n. 1
8, 18, 40, 82, 168, 332, 658, 1282, 2506, 4860, 9454, 18332, 35644, 69254, 134882, 262834, 513264, 1003378, 1965216, 3853972, 7570530, 14890218, 29329178, 57838732, 114202070, 225732564, 446654196, 884613318, 1753564890, 3478856050 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
FORMULA
Empirical: a(n) = 3*a(n-1) + 2*a(n-2) - 11*a(n-3) + 2*a(n-4) + 10*a(n-5) - 4*a(n-6).
Empirical g.f.: 2*x*(4 - 3*x - 15*x^2 + 7*x^3 + 12*x^4 - 6*x^5) / ((1 - 2*x)*(1 - 2*x^2)*(1 - x - 2*x^2 + x^3)). - Colin Barker, Jul 18 2018
EXAMPLE
Some solutions for n=5:
..0....0...-1...-1...-1...-1....0....0...-1...-1...-1....0....1....1....1....0
..1...-1....0...-1....1....1...-1....1....0....1...-1...-1....0....0....1...-1
..0....1...-1...-1....0....0....0....0....1....0...-1....1....1...-1....1....1
.-1....1....1....1...-1...-1...-1....1....0....1...-1....1....0....0...-1....1
..0....1...-1...-1....1....1....1...-1....1...-1...-1....1...-1....1....0...-1
.-1...-1....1...-1...-1....0....0...-1....0....1...-1....1....0...-1...-1....0
CROSSREFS
Sequence in context: A134062 A251251 A067563 * A123134 A096283 A300524
KEYWORD
nonn
AUTHOR
R. H. Hardin, Apr 12 2012
STATUS
approved

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Last modified July 22 08:35 EDT 2024. Contains 374485 sequences. (Running on oeis4.)