A160597 - OEIS

%I #18 Sep 08 2022 08:45:45

%S 1,2,3,4,5,6,7,8,3,10,11,12,13,2,15,16,17,18,19,20,7,22,23,24,25,26,

%T 27,28,29,30,31,32,11,34,35,36,37,38,13,40,41,42,43,44,15,46,47,48,49,

%U 50,51,52,53,18,55,8,19,58,59,60,61,62,63,64,65,66,67,68,3,70,71,72,73,74

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

%C Obviously C(p) = 1/(p-1) for all primes p.

%H Robert Israel, <a href="/A160597/b160597.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)=3 since for n=10, we have (n - phi(n))/(n-1) = (10-4)/9 = 2/3.

%p seq(denom((n-numtheory:-phi(n))/(n-1)),n=2..100); # _Robert Israel_, Dec 26 2016

%t Denominator[Table[(n - EulerPhi[n])/(n - 1), {n, 2, 20}]] (* _G. C. Greubel_, Dec 26 2016 *)

%o (PARI) A160597(n)=denominator((n-eulerphi(n))/(n-1))

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

%Y Cf. A160598.

%K nonn,frac,look

%O 2,2

%A _M. F. Hasler_, May 23 2009