OFFSET
1,1
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..1000
FORMULA
G.f.: -2 * Sum_{k>=1} phi(k) * log(1 - 2*x^k) / k. - Ilya Gutkovskiy, Apr 15 2021
a(n) = 2*A000031(n). - Hugo Pfoertner, Jun 24 2021
PROG
(PARI) a(n) = sumdiv(n, d, eulerphi(n/d)*2^(d+1))/n; \\ Michel Marcus, Apr 15 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Nov 21 2009
STATUS
approved