login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A072209 Number of primitive roots of those integers with at least one primitive root. 2
1, 1, 1, 1, 2, 1, 2, 2, 2, 4, 4, 2, 8, 2, 6, 4, 10, 8, 4, 6, 12, 8, 8, 12, 6, 16, 12, 10, 22, 12, 8, 24, 6, 12, 28, 16, 8, 20, 24, 24, 12, 24, 18, 16, 40, 12, 40, 22, 32, 12, 40, 32, 24, 52, 36, 48, 28, 40, 16, 40, 36, 48, 20, 64, 44, 24, 24, 72, 40, 48, 24, 18, 54 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

COMMENTS

Essentially sequence A046144 with all zero entries deleted.

LINKS

T. D. Noe, Table of n, a(n) for n=1..10000

FORMULA

a(n) = phi(phi(A033948(n))).

MATHEMATICA

Reap[ Do[ If[n == 1, Sow[1], If[ IntegerQ[ PrimitiveRoot[n]], Sow[ EulerPhi[ EulerPhi[n]]]]] , {n, 1, 100}]][[2, 1]] (* Jean-Fran├žois Alcover, Feb 24 2012 *)

PROG

(PARI) is(n)=if(n%2, isprimepower(n) || n==1, n==2 || n==4 || (isprimepower(n/2, &n) && n>2));

lista(nn) = for (n=1, nn, if (is(n), print1(eulerphi(eulerphi(n)), ", "))); \\ Michel Marcus, May 12 2017

CROSSREFS

Cf. A033948, A046144.

Sequence in context: A208216 A208217 A009213 * A226559 A060169 A117958

Adjacent sequences:  A072206 A072207 A072208 * A072210 A072211 A072212

KEYWORD

nice,nonn

AUTHOR

Lekraj Beedassy, Jul 03 2002

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.

License Agreements, Terms of Use, Privacy Policy .

Last modified July 23 10:44 EDT 2017. Contains 289686 sequences.