OFFSET
1,3
FORMULA
G.f.: -Sum_{k>=1} mu(11 * k) * x^k / (1 - x^k)^2, where mu() is the Moebius function (A008683).
Multiplicative with a(11^e) = 11^e, and a(p^e) = (p-1)*p^(e-1) if p != 11.
Sum_{k=1..n} a(k) ~ (121/(40*Pi^2)) * n^2. - Amiram Eldar, May 10 2024
MATHEMATICA
a[n_] := EulerPhi[11 * n]/10; Array[a, 100] (* Amiram Eldar, May 10 2024 *)
PROG
(PARI) a(n) = eulerphi(11*n)/10;
(PARI) my(N=80, x='x+O('x^N)); Vec(-sum(k=1, N, moebius(11*k)*x^k/(1-x^k)^2))
CROSSREFS
KEYWORD
nonn,mult,easy
AUTHOR
Seiichi Manyama, May 10 2024
STATUS
approved