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A049117 Smallest number which when Euler phi function is repeatedly applied have not reached a power of 2 in n steps. 3
3, 7, 19, 47, 163, 487, 1307, 2879, 19683, 39367, 177147, 531441, 1594323, 4782969, 14348907, 43046721, 86093443, 258280327, 688747547, 3486784401, 10460353203 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

a(21) <= 31381059609 = 3^22. [Donovan Johnson, Feb 06 2010]

Note that all terms so far are primes or powers of 3. Is it true that all terms have this form? - T. D. Noe, Oct 07 2013

LINKS

Table of n, a(n) for n=0..20.

EXAMPLE

The corresponding iterated phi-sequences are:

{3, 2, 1},

{7, 6, 2, 1},

{19, 18, 6, 2, 1},

{47, 46, 22, 10, 4, 2, 1},

{163, 162, 54, 18, 6, 2, 1},

{487, 486, 162, 54, 18, 6, 2, 1}, ...

MATHEMATICA

a[n_] := Module[{i = 1}, While[IntegerQ[Log[2, Nest[EulerPhi, i, n]]], i++ ]; i]; (* Sam Handler (sam_5_5_5_0(AT)yahoo.com), Sep 04 2006 *)

CROSSREFS

A variant of A227946.

Cf. A000010.

Sequence in context: A181360 A001372 A179467 * A146810 A246493 A293733

Adjacent sequences:  A049114 A049115 A049116 * A049118 A049119 A049120

KEYWORD

nonn,more

AUTHOR

Labos Elemer

EXTENSIONS

More terms from Jud McCranie, Jan 14 2000

More terms from Sam Handler (sam_5_5_5_0(AT)yahoo.com), Sep 04 2006

a(19)-a(20) from Donovan Johnson, Feb 06 2010

STATUS

approved

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Last modified August 14 21:07 EDT 2018. Contains 313756 sequences. (Running on oeis4.)