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%I #13 Jul 18 2021 01:54:40
%S 8,115,187,1375,2455,8143,13543,18261,21103,23479,40615,41623,43279,
%T 49183,49441,51703,56743,61063,61279,61423,89287,95551,137887,214303,
%U 331567,379807,476071,715471,1422871,1515967,1793527,1977127,2431087,3098527,3663871
%N Numbers k such that sigma(k) - k - 1 is a perfect number.
%e sigma(8) - 8 - 1 = 6, a perfect number, so 8 is a term;
%e sigma(115) - 115 - 1 = 28, a perfect number, so 115 is a term.
%t With[{pn=PerfectNumber[Range[10]]},Select[Range[37*10^5],MemberQ[pn, DivisorSigma[ 1,#]-#-1]&]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Feb 04 2019 *)
%Y Cf. A000396, A048050.
%K nonn
%O 1,1
%A _Zdenek Cervenka_, Oct 21 2017