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A071181 Number of k such that phi(k) divides phi(n). 2

%I

%S 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,

%T 11,14,13,20,16,20,34,19,31,13,34,20,30,19,13,16,34,7,7,20,13,16,27,

%U 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

%N Number of k such that phi(k) divides phi(n).

%H Antti Karttunen, <a href="/A071181/b071181.txt">Table of n, a(n) for n = 1..2048</a> (computed with the help of b-file of A057826 provided by T. D. Noe)

%F For all n, a(n) >= A066412(n). - _Antti Karttunen_, Jul 17 2017

%o (PARI) for(n=1,100,print1(sum(i=1,1000,if(eulerphi(n)%eulerphi(i),0,1)),","))

%o (Scheme)

%o ;; A naive implementation requiring precomputed A057826:

%o (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

%Y Cf. A000010, A057826, A066412.

%K easy,nonn

%O 1,1

%A _Benoit Cloitre_, Jun 10 2002

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Last modified August 17 07:46 EDT 2017. Contains 290635 sequences.