OFFSET
1,2
FORMULA
a(n) = Sum_{d|n} phi(n/d) * tau(d)^d.
If p is prime, a(p) = 2^p - 1 + p.
MATHEMATICA
a[n_] := DivisorSum[n, EulerPhi[n/#] * DivisorSigma[0, #]^# &]; Array[a, 26] (* Amiram Eldar, May 11 2021 *)
PROG
(PARI) a(n) = sum(k=1, n, numdiv(gcd(k, n))^gcd(k, n));
(PARI) a(n) = sumdiv(n, d, eulerphi(n/d)*numdiv(d)^d);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, May 11 2021
STATUS
approved