OFFSET
1,1
COMMENTS
Every even superperfect number (A019279) is a term of the sequence. - Vladeta Jovovic, Feb 11 2002
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..1000
MAPLE
with(numtheory); A067709:=n->`if`( phi(2*sigma(n)) = 2*sigma(phi(n)), n, NULL); seq(A067709(n), n=1..200000); # Wesley Ivan Hurt, Apr 07 2014
MATHEMATICA
Select[Range[200000], EulerPhi[2*DivisorSigma[1, #]] == 2*DivisorSigma[1, EulerPhi[#]] &] (* Amiram Eldar, May 13 2022 *)
PROG
(PARI) isok(k) = eulerphi(2*sigma(k)) == 2*sigma(eulerphi(k)); \\ Michel Marcus, May 13 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Feb 05 2002
EXTENSIONS
More terms from Vladeta Jovovic, Feb 11 2002
STATUS
approved