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%I #37 Dec 02 2019 15:21:09
%S 12,70,88,180,1888,4030,5830,32128,521728,1848964,8378368,34359083008,
%T 66072609790,549753192448,259708613909470
%N Numbers k such that sigma(k) == 0 (mod k+2).
%C a(12) > 10^8. - _Michel Marcus_, Nov 22 2013
%C If 2^i-5 is prime for i > 2 then let x = (2^i-5)*2^(i-1). Then sigma(x)=2*(x+2), so x is in the sequence. There are other terms that are not of this form. - _Jud McCranie_, Jan 12 2019
%e sigma(180) = 546 = 3(180+2), so 180 is in the sequence.
%t Select[Range[84*10^5],Divisible[DivisorSigma[1,#],#+2]&] (* _Harvey P. Dale_, May 11 2018 *)
%o (PARI) isok(n) = sigma(n) % (n+2) == 0; \\ _Michel Marcus_, Nov 22 2013
%Y Cf. A045768, A156560, A059608.
%K nonn,more
%O 1,1
%A _Benoit Cloitre_, Feb 05 2002
%E a(9)-a(11) from _Michel Marcus_, Nov 22 2013
%E a(12)-a(13) from _Jud McCranie_, Jan 12 2019
%E a(14) from _Jud McCranie_, Jan 13 2019
%E a(15) from _Jud McCranie_, Dec 02 2019