|
%I #14 Jul 04 2021 11:41:10
%S 1,2,2,3,3,4,4,5,5,5,5,6,6,6,6,7,7,8,8,8,8,8,8,9,9,9,9,9,9,9,9,10,10,
%T 10,10,11,11,11,11,11,11,11,11,11,11,11,11,12,12,12,12,12,12,13,13,13,
%U 13,13,13,13,13,13,13,14,14,14,14,14,14,14,14,15,15,15,15,15,15,15,15
%N Number of k, 1<=k<=n, such that phi(k) divides k.
%H Vaclav Kotesovec, <a href="/A069924/b069924.txt">Table of n, a(n) for n = 1..10000</a>
%H Vaclav Kotesovec, <a href="/A069924/a069924.jpg">Plot of a(n)/log(n)^2 for n = 1..10000</a>
%F a(n) = Card(k: 1<=k<=n : k==0 (mod phi(k))) asymptotically: a(n) = C*log(n)^2 + o(log(n)^2) with C=0.6....
%t Table[Length[Select[Range[n], Divisible[#, EulerPhi[#]] &]], {n, 1, 100}] (* _Vaclav Kotesovec_, Feb 16 2019 *)
%t Accumulate[Table[If[Divisible[n,EulerPhi[n]],1,0],{n,80}]] (* _Harvey P. Dale_, Jul 04 2021 *)
%o (PARI) for(n=1,150,print1(sum(i=1,n,if(i%eulerphi(i),0,1)),","))
%K easy,nonn
%O 1,2
%A _Benoit Cloitre_, May 05 2002
|
