A090778 Numbers k such that phi(k) divides k*(k - phi(k)).

1, 2, 4, 6, 8, 10, 12, 16, 18, 20, 24, 32, 36, 40, 42, 48, 50, 54, 60, 64, 72, 80, 84, 96, 100, 108, 114, 120, 126, 128, 136, 144, 156, 160, 162, 168, 180, 192, 200, 216, 220, 228, 240, 250, 252, 256, 272, 288, 294, 300, 312, 320, 324, 336, 342, 360, 378, 384, 400

Offset

1,2

Comments

Also phi(k) divides k^2. - Enrique Pérez Herrero, Jul 04 2010

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Formula

a(n) seems to be asymptotic to c*n^2 with c=0.11.....

Mathematica

pdnQ[n_]:=Module[{ephi=EulerPhi[n]}, Divisible[n(n-ephi), ephi]]; Select[ Range[ 400], pdnQ] (* Harvey P. Dale, Dec 22 2015 *)

Crossrefs

Sequence in context: A071594 A306263 A071596 * A097380 A114270 A109884

Adjacent sequences: A090775 A090776 A090777 * A090779 A090780 A090781

Keyword

nonn

Author

Benoit Cloitre, Feb 08 2004

Status

approved