OFFSET
1,3
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
Olivier Bordellès and Benoit Cloitre, An Alternating Sum Involving the Reciprocal of Certain Multiplicative Functions, J. Int. Seq., Vol. 16 (2013) Article #13.6.3.
FORMULA
A211177(n)/a(n) = c*log(n) + O(1) with a suitable constant c (see ref).
The constant above is c = zeta(2)*zeta(3)/(3*zeta(6)) = (1/3) * A082695. - Amiram Eldar, Nov 20 2020
MATHEMATICA
Denominator @ Accumulate[Table[(-1)^k/EulerPhi[k], {k, 1, 50}]] (* Amiram Eldar, Nov 20 2020 *)
PROG
(PARI) a(n)=denominator(sum(k=1, n, (-1)^k/eulerphi(k)))
CROSSREFS
KEYWORD
nonn,frac
AUTHOR
Benoit Cloitre, Feb 01 2013
EXTENSIONS
More terms from Amiram Eldar, Nov 20 2020
STATUS
approved