OFFSET
1,2
COMMENTS
Inverse Moebius transform of A006874.
FORMULA
G.f. A(x) satisfies: A(x) = x / (1 - x) + Sum_{k>=2} phi(k) * A(x^k).
a(n) = 1 + Sum_{d|n, d < n} phi(n/d) * a(d).
a(n) = Sum_{d|n} A006874(d).
MATHEMATICA
a[n_] := a[n] = 1 + Sum[a[GCD[n, k]], {k, 1, n - 1}]; Table[a[n], {n, 1, 63}]
a[n_] := a[n] = 1 + DivisorSum[n, EulerPhi[n/#] a[#] &, # < n &]; Table[a[n], {n, 1, 63}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Nov 06 2020
STATUS
approved