OFFSET
1,3
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
a(2^e) = 2 for e > 1.
a(p^e) = 2 for an odd prime p and e > 0.
a(n) >= omega(n), with equality if and only if n is in A278568.
EXAMPLE
MATHEMATICA
f[p_, e_] := p^e - 1; uphi[1] = 1; uphi[n_] := Times @@ f @@@ FactorInteger[n]; a[n_] := Length @ Union[uphi /@ Select[Divisors[n], CoprimeQ[#, n/#] &]]; Array[a, 100]
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Sep 23 2021
STATUS
approved