OFFSET
1,5
LINKS
FORMULA
If n = Product (p_j^k_j) then a(n) = Sum (phi(pi(p_j))).
MATHEMATICA
nmax = 85; CoefficientList[Series[Sum[EulerPhi[k] x^Prime[k]/(1 - x^Prime[k]), {k, 1, nmax}], {x, 0, nmax}], x] // Rest
a[n_] := Plus @@ (EulerPhi[PrimePi[#[[1]]]] & /@ FactorInteger[n]); Table[a[n], {n, 85}]
PROG
(PARI) a(n) = my(f=factor(n)); sum(k=1, #f~, eulerphi(primepi(f[k, 1]))); \\ Michel Marcus, Apr 03 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Apr 02 2020
STATUS
approved