OFFSET
1,1
LINKS
M. F. Hasler and Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 (first 110 terms from Hasler)
MATHEMATICA
Select[Range[3000], EulerPhi[DivisorSigma[1, #]]==2EulerPhi[#]&] (* Harvey P. Dale, Oct 15 2020 *)
PROG
(PARI) is(n)=2*eulerphi(n=factor(n))==eulerphi(sigma(n)) \\ Charles R Greathouse IV, Nov 27 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Feb 05 2002
STATUS
approved