OFFSET
0,4
COMMENTS
The graph is empty for n = 0, 1 and 2, so a(n) = 0 by convention (or should it be 1?).
REFERENCES
A. Iranmanesh and A. Jafarzadeh, On the commuting graph associated with the symmetric and alternating groups, J. Algebra and Applic., 7 (2008), 129-146.
FORMULA
Conjecture: a(n) = a(n-1) + 3*a(n-3) - 3*a(n-4) for n>7; g.f.: -x^3*(3*x^3 - 2*x^2 - x - 2) / ((x-1)*(3*x^3-1)). - Colin Barker, Jul 26 2013
MATHEMATICA
f[n_]:=n+Divisors[n+1][[Length[Divisors[n+1]]-1]]; a=1; Table[a=f[a], {n, 5!}] (* Vladimir Joseph Stephan Orlovsky, Mar 03 2010 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Mar 07 2008
STATUS
approved