OFFSET
1,2
FORMULA
From Richard L. Ollerton, May 06 2021: (Start)
a(n) = Sum_{d|n} phi(d)*A000110(n/d) (by definition).
a(n) = Sum_{k=1..n} A000110(gcd(n,k)).
a(n) = Sum_{k=1..n} A000110(n/gcd(n,k))*phi(gcd(n,k))/phi(n/gcd(n,k)). (End)
MATHEMATICA
Table[Sum[BellB[n/d - 1]*EulerPhi[d], {d, Divisors[n]}], {n, 1, 25}] (* Vaclav Kotesovec, Sep 10 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved