|
|
A211525
|
|
Number of -1..1 arrays x(i) of n+1 elements i=1..n+1 with set{t,u,v in 0,1}((x[i+t]+x[j+u]+x[k+v])*(-1)^(t+u+v)) having two or four distinct values for every i,j,k<=n.
|
|
2
|
|
|
8, 14, 24, 44, 80, 152, 288, 560, 1088, 2144, 4224, 8384, 16640, 33152, 66048, 131840, 263168, 525824, 1050624, 2100224, 4198400, 8394752, 16785408, 33566720, 67125248, 134242304, 268468224, 536920064, 1073807360, 2147581952, 4295098368
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
LINKS
|
|
|
FORMULA
|
Empirical: a(n) = 2*a(n-1) + 2*a(n-2) - 4*a(n-3).
G.f.: 2*x*(4 - x - 10*x^2) / ((1 - 2*x)*(1 - 2*x^2)).
a(n) = 3*2^(n/2) + 2^(n+1) for n even.
a(n) = 2^(n+1) + 2^((n+3)/2) for n odd.
(End)
|
|
EXAMPLE
|
Some solutions for n=5:
.-1....1....1...-1....1....0....1...-1...-1...-1....1...-1...-1....0....0...-1
..1....0....1...-1....0...-1....1....0....1...-1....1...-1....1....1...-1....0
.-1...-1...-1....1...-1....0....1...-1....1....1....1....1...-1....0....0...-1
..1....0...-1...-1....0....1...-1....0...-1....1...-1...-1....1...-1....1....0
.-1...-1...-1...-1....1....0....1...-1...-1...-1...-1....1....1....0....0....1
..1....0....1....1....0...-1...-1....0....1...-1....1....1....1...-1....1....0
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|