A331273 Sum of the iterated exponential totient function (A072911).

0, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 3, 1, 1, 1, 1, 5, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 3, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 3, 3, 1, 1, 1, 1, 1, 1

Offset

1,8

Comments

Analogous to A092693 with the exponential totient function ephi instead of the Euler totient function phi (A000010).

a(n) = 1 for n > 1 which is cubefree (A004709) and a(n) > 1 for n in A046099.

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Example

a(8) = ephi(8) + ephi(ephi(8)) = 2 + 1 = 3 (where ephi is A072911).

Mathematica

ephi[n_] := Times @@ EulerPhi[FactorInteger[n][[;; , 2]]]; s[n_] := Plus @@ FixedPointList[ephi, n] - n - 1; Array[s, 100]

Crossrefs

Cf. A004709, A046099, A072911, A092693.

Sequence in context: A185358 A368247 A372604 * A363332 A372601 A333843

Adjacent sequences: A331270 A331271 A331272 * A331274 A331275 A331276

Keyword

nonn

Author

Amiram Eldar, Feb 25 2020

Status

approved