

A049108


a(n) is the number of iterations of Euler phi function needed to reach 1 starting at n (n is counted).


21



1, 2, 3, 3, 4, 3, 4, 4, 4, 4, 5, 4, 5, 4, 5, 5, 6, 4, 5, 5, 5, 5, 6, 5, 6, 5, 5, 5, 6, 5, 6, 6, 6, 6, 6, 5, 6, 5, 6, 6, 7, 5, 6, 6, 6, 6, 7, 6, 6, 6, 7, 6, 7, 5, 7, 6, 6, 6, 7, 6, 7, 6, 6, 7, 7, 6, 7, 7, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 7, 6, 7, 8, 6, 8, 6, 7, 7, 8, 6, 7, 7, 7, 7, 7, 7, 8, 6, 7, 7, 8, 7, 8, 7, 7
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OFFSET

1,2


LINKS

R. Zumkeller, Table of n, a(n) for n = 1..10000


FORMULA

By the definition of a(n) we have for n >= 2 the recursion a(n) = a(Phi(n)) + 1.  Ahmed Fares (ahmedfares(AT)mydeja.com), Apr 20 2001
log_3 n << a(n) << log_2 n.  Charles R Greathouse IV, Feb 07 2012


EXAMPLE

If n=164 the trajectory is {164,80,32,16,8,4,2,1}. Its length is 8, thus a(164)=8.


MATHEMATICA

f[n_] := Length[NestWhileList[ EulerPhi, n, # != 1 &]]; Array[f, 105] (* Robert G. Wilson v, Feb 07 2012 *)


PROG

(PARI) a(n)=my(t=1); while(n>1, t++; n=eulerphi(n)); t \\ Charles R Greathouse IV, Feb 07 2012


CROSSREFS

Cf. A000010, A007755. Equals A003434 + 1.
Sequence in context: A305716 A297616 A213251 * A179846 A086925 A088858
Adjacent sequences: A049105 A049106 A049107 * A049109 A049110 A049111


KEYWORD

nonn,nice,easy


AUTHOR

Labos Elemer


STATUS

approved



