login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A071181 Number of k such that phi(k) divides phi(n). 6
2, 2, 5, 5, 9, 5, 9, 9, 9, 9, 7, 9, 19, 9, 14, 14, 20, 9, 13, 14, 19, 7, 7, 14, 16, 19, 13, 19, 11, 14, 13, 20, 16, 20, 34, 19, 31, 13, 34, 20, 30, 19, 13, 16, 34, 7, 7, 20, 13, 16, 27, 34, 11, 13, 30, 34, 31, 11, 7, 20, 37, 13, 31, 27, 51, 16, 13, 27, 14, 34, 9, 34, 63, 31, 30, 31 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..2048 (computed with the help of b-file of A057826 provided by T. D. Noe)
FORMULA
For all n, a(n) >= A066412(n). - Antti Karttunen, Jul 17 2017
PROG
(PARI) for(n=1, 100, print1(sum(i=1, 1000, if(eulerphi(n)%eulerphi(i), 0, 1)), ", "))
(Scheme)
;; A naive implementation requiring precomputed A057826:
(define (A071181 n) (if (<= n 2) 2 (let ((ph (A000010 n))) (let loop ((k (A057826 (/ ph 2))) (s 0)) (if (zero? k) s (loop (- k 1) (+ s (if (zero? (modulo ph (A000010 k))) 1 0)))))))) ;; Antti Karttunen, Jul 18 2017
CROSSREFS
Sequence in context: A345165 A062405 A368180 * A213675 A321185 A320322
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Jun 10 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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 21 13:52 EST 2024. Contains 370235 sequences. (Running on oeis4.)