A348213 - OEIS

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A348213

a(n) is the number of iterations that n requires to reach a fixed point under the map x -> A348158(x).

0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 1, 2, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 2, 0, 1, 0, 1, 0, 1, 0

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OFFSET

1,64

COMMENTS

a(n) first differs from 1-A000035(n) at n = 63.

The number of iterations is finite for all n since A348158(n) <= n.

The fixed points are terms of A326835, so a(n) = 0 if and only if n is a term of A326835.

LINKS

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

EXAMPLE

a(1) = 0 since 1 is in A326835.

a(2) = 1 since there is one iteration of the map x -> A348158(x) starting from 2: 2 -> 1.

a(64) = 2 since there are 2 iterations of the map x -> A348158(x) starting from 64: 64 -> 63 -> 57.

MATHEMATICA

f[n_] := Plus @@ DeleteDuplicates @ Map[EulerPhi, Divisors[n]]; a[n_] := -2 + Length @ FixedPointList[f, n]; Array[a, 100]

PROG

(Python)

from sympy import totient, divisors

def A348213(n):

c, k = 0, n

m = sum(set(map(totient, divisors(k, generator=True))))

while m != k:

k = m

m = sum(set(map(totient, divisors(k, generator=True))))

c += 1

return c # Chai Wah Wu, Nov 15 2021

CROSSREFS

Cf. A000035, A003434, A326835, A348158.

Sequence in context: A123671 A191261 A355745 * A355741 A355744 A179010

Adjacent sequences: A348210 A348211 A348212 * A348214 A348215 A348216

KEYWORD

nonn

AUTHOR

Amiram Eldar, Oct 07 2021

STATUS

approved