A069924 Number of k, 1<=k<=n, such that phi(k) divides k.

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, 10, 10, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 12, 12, 12, 12, 12, 12, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 14, 14, 14, 14, 14, 14, 14, 14, 15, 15, 15, 15, 15, 15, 15, 15

Offset

1,2

Links

Vaclav Kotesovec, Table of n, a(n) for n = 1..10000

Vaclav Kotesovec, Plot of a(n)/log(n)^2 for n = 1..10000

Formula

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....

Mathematica

Table[Length[Select[Range[n], Divisible[#, EulerPhi[#]] &]], {n, 1, 100}] (* Vaclav Kotesovec, Feb 16 2019 *)
Accumulate[Table[If[Divisible[n, EulerPhi[n]], 1, 0], {n, 80}]] (* Harvey P. Dale, Jul 04 2021 *)

Prog

(PARI) for(n=1, 150, print1(sum(i=1, n, if(i%eulerphi(i), 0, 1)), ", "))

Crossrefs

Sequence in context: A085089 A228720 A219652 * A225559 A082479 A090616

Adjacent sequences: A069921 A069922 A069923 * A069925 A069926 A069927

Keyword

easy,nonn

Author

Benoit Cloitre, May 05 2002

Status

approved