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

 

Logo

Annual appeal: Please make a donation to keep the OEIS running! Over 6000 articles have referenced us, often saying "we discovered this result with the help of the OEIS".
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A071181 Number of k such that phi(k) divides phi(n). 4
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

Cf. A000010, A057826, A066412.

Sequence in context: A222706 A240495 A062405 * A213675 A214795 A287744

Adjacent sequences:  A071178 A071179 A071180 * A071182 A071183 A071184

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 | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified December 17 04:09 EST 2017. Contains 296096 sequences.