OFFSET
1,1
FORMULA
See Maple code for formula.
EXAMPLE
a(2) = 4, the labelings being {000}, {001}, {011}, {111}. Some of the 20 solutions for n=3 are as follows:
..0......1.......0......1.......1.......1.......0
.0.0....0.0.....1.0....1.0.....0.0.....0.0.....1.1
0.0.0..0.0.0...0.0.0..0.0.0...1.0.0...0.1.0...0.0.0
The first solution for n = 4 is
...0
..0.0
.0.0.0
0.0.0.0
MAPLE
A061348 := proc(n) local t1, v, a; a := n*(n+1)/2; v := floor((n+1)/2); if n mod 3 = 1 then t1 := n*(n+1)/6+2/3; else t1 := n*(n+1)/6; fi; (1/6)*(2^a + 2*2^t1+3*2^(a/2+v/2)); end; # from Burnside's Lemma
MATHEMATICA
A061348[n_] := Module[{t1, v, a}, a = n*(n+1)/2; v = Floor[(n+1)/2]; If[Mod[n, 3] == 1, t1 = n*(n+1)/6+2/3, t1 = n*(n+1)/6]; (1/6)*(2^a+2*2^t1+3*2^(a/2+v/2))]; Table[A061348[n], {n, 1, 15}] (* Jean-François Alcover, Feb 03 2014, after Maple *)
CROSSREFS
KEYWORD
nonn,easy,nice
AUTHOR
Michel ten Voorde, Jun 08 2001
EXTENSIONS
Formula and more terms from N. J. A. Sloane, Jun 20 2001
STATUS
approved