OFFSET
1,6
COMMENTS
This sequence appears to be nonnegative. However, a proof of this has not yet been found.
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..1000
FORMULA
For prime p, a(p) = 0 (see A113166 for details).
MATHEMATICA
a[n_] := Sum[ k/(n - k)*Sum[ Binomial[(n - k)*GCD[n, k, j]/GCD[n, k],
k*GCD[n, k, j]/GCD[n, k]], {j, 1, GCD[n, k]}], {k, 1, Floor[n/2]}];
Table[a[n] - Fibonacci[n - 1], {n, 1, 50}] (* G. C. Greubel, Mar 12 2017 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Creighton Dement, Jan 09 2006; corrected Jun 20 2006
EXTENSIONS
More terms from R. J. Mathar, Feb 08 2008
More terms from Max Alekseyev, Jun 06 2009
STATUS
approved