A160598 - OEIS

%I #14 Sep 08 2022 08:45:45

%S 1,1,2,1,4,1,4,3,2,1,8,1,8,1,8,1,12,1,12,9,4,1,16,5,14,9,16,1,22,1,16,

%T 13,6,11,24,1,20,15,8,1,30,1,24,21,8,1,32,7,30,19,28,1,36,5,32,3,10,1,

%U 44,1,32,27,32,17,46,1,36,25,2,1,48,1,38,35,8,17,54,1,48,27,14,1,60,1

%N Numerator of coresilience C(n) = (n - phi(n))/(n-1).

%C Obviously C(p) = 1/(p-1), i.e., a(p)=1, for all primes p. Sequence A160599 lists composite numbers for which this is the case.

%H Vincenzo Librandi, <a href="/A160598/b160598.txt">Table of n, a(n) for n = 2..10000</a>

%H Project Euler, <a href="http://projecteuler.net/index.php?section=problems&amp;id=245">Problem 245: resilient fractions</a>, May 2009

%e a(10)=2 since for n=10, we have (n - phi(n))/(n-1) = (10-4)/9 = 2/3.

%t Numerator[Table[(n - EulerPhi[n])/(n - 1), {n, 2, 90}]] (* _Vincenzo Librandi_, Dec 27 2016 *)

%o (PARI) A160598(n)=numerator((n-eulerphi(n))/(n-1))

%o (Magma) [Numerator((n-EulerPhi(n))/(n-1)): n in [2..80]]; // _Vincenzo Librandi_, Dec 27 2016

%Y Cf. A160595, A160596, A160597, A160599.

%K nonn,frac

%O 2,3

%A _M. F. Hasler_, May 23 2009