This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 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 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.