OFFSET
1,1
COMMENTS
All terms 2 < a(n) < 20000000 are odd and divisible by 3. Most are squarefree.
From numerical observation if n>31 : log(n)^10 < a(n) < log(n)^11.
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..500
MATHEMATICA
Do[s=DivisorSigma[1, (n-EulerPhi[n])]-EulerPhi[n]; If[Equal[s, 0], Print[n]], {n, 1, 2000000}]
PROG
(PARI) for(n=2, 2000000, if(sigma(n-eulerphi(n))==eulerphi(n), print1(n, ", ")))
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre and Labos Elemer, May 06 2002
EXTENSIONS
Edited by Charles R Greathouse IV, Oct 28 2009
STATUS
approved