OFFSET
1,2
COMMENTS
In general, for m >= 1, Sum_{k=1..n} Sum_{d|k} psi_m(d) = Sum_{k=1..n} k^m * A064608(floor(n/k)), where psi_m(d) is the generalized Dedekind psi function.
Additionally, for m >= 1, Sum_{k=1..n} Sum_{d|k} psi_m(d) ~ (n^(m+1) * zeta(m+1)^2) / ((m+1) * zeta(2*(m+1))).
LINKS
Vaclav Kotesovec, Table of n, a(n) for n = 1..10000
Wikipedia, Dedekind psi function
FORMULA
a(n) ~ (5/4) * n^2.
a(n) = Sum_{k=1..n} A060648(k).
a(n) = Sum_{k=1..n} Sum_{d|k} A001615(d).
a(n) = Sum_{k=1..n} k * A064608(floor(n/k)).
a(n) = (1/2)*Sum_{k=1..n} 2^omega(k) * floor(n/k) * floor(1+n/k).
a(n) = Sum_{k=1..n} A001615(k)*floor(n/k). - Ridouane Oudra, Aug 27 2019
MAPLE
with(numtheory): psi := n -> n*mul(1+1/p, p in factorset(n)):
seq(add(psi(i)*floor(n/i), i=1..n), n=1..80); # Ridouane Oudra, Aug 27 2019
MATHEMATICA
Accumulate[Table[Sum[EulerPhi[n/d] * DivisorSigma[0, d^2], {d, Divisors[n]}], {n, 1, 100}]] (* Vaclav Kotesovec, Oct 09 2019 *)
PROG
(PARI) a(n) = sum(k=1, n, 2^omega(k) * (n\k) * (1+n\k))/2;
CROSSREFS
KEYWORD
nonn
AUTHOR
Daniel Suteu, Mar 09 2019
STATUS
approved