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A331273 Sum of the iterated exponential totient function (A072911). 3
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 (list; graph; refs; listen; history; text; internal format)
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: A031228 A031227 A185358 * A333843 A204129 A204114

Adjacent sequences:  A331270 A331271 A331272 * A331274 A331275 A331276

KEYWORD

nonn

AUTHOR

Amiram Eldar, Feb 25 2020

STATUS

approved

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Last modified September 22 00:42 EDT 2020. Contains 337276 sequences. (Running on oeis4.)