OFFSET
1,1
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Juhani Karhumäki, S. Puzynina, M. Rao, M. A. Whiteland, On cardinalities of k-abelian equivalence classes, arXiv preprint arXiv:1605.03319 [math.CO], 2016.
FORMULA
See Karhumäki et al. (2016), Proposition 7.4.
MATHEMATICA
Table[a=Select[Divisors[n], OddQ[#]&]; (1 + Apply[Plus, 2^(n/a)EulerPhi[a]]/n), {n, 2, 52, 2}] (* Vincenzo Librandi, Mar 29 2017 *)
PROG
(PARI) a(n) = my(m = 2*n); 1 + sumdiv(m, d, (d%2)* 2^(m/d)*eulerphi(d))/m; \\ Michel Marcus, Aug 18 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Mar 28 2017
STATUS
approved