|
|
A088808
|
|
Number of subsets of {1, ..., n} that are not double-free.
|
|
9
|
|
|
0, 0, 1, 2, 6, 12, 34, 68, 160, 320, 736, 1472, 3136, 6272, 13504, 27008, 56176, 112352, 234064, 468128, 954976, 1909952, 3913504, 7827008, 15878656, 31757312, 64413184, 128826368, 259449856, 518899712, 1046785024, 2093570048, 4207876096, 8415752192
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,4
|
|
COMMENTS
|
a(n) = 2^n - A050291(n); a(2*k+1) = a(2*k)*2;
a non-double-free subset contains at least one subset {x,y} with y=2*x.
|
|
LINKS
|
|
|
MATHEMATICA
|
A050291[n_] := A050291[n] = If[n == 1, 2, With[{b = IntegerExponent[2n, 2]}, A050291[n - 1] Fibonacci[b + 2]/Fibonacci[b + 1]]];
a[n_] := If[n == 0, 0, 2^n - A050291[n]];
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|