OFFSET
1,2
FORMULA
If k is squarefree (cf. A005117) then a(k) = k^(k+1).
a(n) = Sum_{d|n} phi(d) * sigma(d^n).
PROG
(PARI) a(n) = sumdiv(n, d, eulerphi(d)*sigma(d^n));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, May 19 2024
STATUS
approved