OFFSET
1,1
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
Jean-Marie De Koninck and Florian Luca, Positive integers n such that sigma(phi(n)) = sigma(n), Journal of Integer Sequences, Paper No. 08.1.5, 2008.
EXAMPLE
a(1) = 2318, because this is the smallest integer such that sigma(2*phi(n)) = 2*sigma(n).
MATHEMATICA
Select[Range[90000], DivisorSigma[1, 2*EulerPhi[#]]==2*DivisorSigma[1, #]&] (* Harvey P. Dale, Jan 31 2015 *)
PROG
(PARI) is(n)=sigma(2*eulerphi(n))==2*sigma(n) \\ Charles R Greathouse IV, Feb 04 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Jeffrey Shallit, Feb 09 2008; definition corrected Feb 09 2008
STATUS
approved