OFFSET
1,2
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..1000
MATHEMATICA
Select[Range[25000], EulerPhi[2#-1]==DivisorSigma[1, #]&] (* Harvey P. Dale, Aug 22 2015 *)
PROG
(PARI) isok(n) = eulerphi(2*n-1) == sigma(n); \\ Michel Marcus, Nov 21 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Feb 20 2002
STATUS
approved