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.
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
Offset: 1
Keywords
Examples
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
Links
- R. H. Hardin, Table of n, a(n) for n = 1..79
Formula
Empirical: a(n) = 2*a(n-1) + 2*a(n-2) - 4*a(n-3).
From Colin Barker, Mar 09 2018: (Start)
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)