OFFSET
1,1
MATHEMATICA
Select[Range[200000], DivisorSigma[1, #-1]+DivisorSigma[1, #+1] == 6*EulerPhi[#]&] (* Harvey P. Dale, May 07 2014 *)
PROG
(PARI) isok(m) = (m>1) && (sigma(m+1)+sigma(m-1) == 6*eulerphi(m)); \\ Michel Marcus, Feb 17 2021
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Feb 20 2002
EXTENSIONS
More terms from Michel Marcus, Feb 17 2021
STATUS
approved