A067680 - OEIS

%I #19 Apr 09 2020 01:55:50

%S 6,21,54,75,441,1071,4191,9315,58311,4197375,7685151,36997695,

%T 268460031,1073790975,17180065791,13517087570210304,18014398710808575,

%U 288230376957018111

%N Numbers k such that sigma(2k + 2) = 4k.

%C If k is a term, then 2*k + 2 is a term of A125246. - _Jinyuan Wang_, Apr 08 2020

%o (PARI) isok(k) = sigma(2*k+2) == 4*k; \\ _Michel Marcus_, Apr 06 2020

%Y Cf. A000203, A125246.

%K nonn,more

%O 1,1

%A _Benoit Cloitre_, Feb 04 2002

%E a(9) from _Benoit Cloitre_ and Neven Juric (neven.juric(AT)apis-it.hr), May 21 2004

%E a(10)-a(15) from _Donovan Johnson_, Jan 31 2009

%E a(16)-a(18) from _Jinyuan Wang_, Apr 06 2020