OFFSET
1,1
MATHEMATICA
Do[s=(DivisorSigma[1, n]+DivisorSigma[1, n+1])/ DivisorSigma[1, 2*n+1]; If[Equal[s, 2], Print[n]], {n, 1, 10000000}]
PROG
(PARI) isok(n) = sigma(n) + sigma(n+1) == 2*sigma(2*n+1); \\ Michel Marcus, Jul 29 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Feb 16 2004
EXTENSIONS
a(16)-a(27) from Donovan Johnson, Jan 31 2009
a(28)-a(31) from Amiram Eldar, May 23 2022
STATUS
approved