OFFSET
1,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..5000
FORMULA
G.f.: Sum_{k>=1} x^k/(1-phi(k)*x^k).
From Seiichi Manyama, Mar 13 2021: (Start)
a(n) = Sum_{k=1..n} phi(n/gcd(k, n))^(gcd(k, n) - 2).
If p is prime, a(p) = 2. (End)
PROG
(PARI) a(n) = sumdiv(n, d, eulerphi(d)^(n/d-1)); \\ Seiichi Manyama, Mar 13 2021
(PARI) a(n) = sum(k=1, n, eulerphi(n/gcd(k, n))^(gcd(k, n)-2)); \\ Seiichi Manyama, Mar 13 2021
(PARI) my(N=66, x='x+O('x^N)); Vec(sum(k=1, N, x^k/(1-eulerphi(k)*x^k))) \\ Seiichi Manyama, Mar 13 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Franklin T. Adams-Watters, Sep 01 2009
STATUS
approved