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
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Feb 08 2004
STATUS
approved