This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A177012 #17 Feb 09 2021 01:57:41
%S A177012 1,2,3,15,87,255,11759,26279,39455,43919,65535,112895,443807,1347455,
%T A177012 1464911,1568255,1604559,1968095,2441559,5948799,16210655,39624767,
%U A177012 39839039,59187455,81624279,83623935,251009695,256685439,338979839,434357967,455345855,471783935,487722815,518291135,596835839
%N A177012 Numbers k such that k^k == -1 (mod phi(k)).
%C A177012 3 is the largest prime term of this sequence.
%C A177012 All terms are squarefree. There is no further term up to 2*10^8.
%C A177012 If phi(k) divides k+1 then k is in the sequence. This implies A050474 and A203966 are subsequences of this sequence. - _Jahangeer Kholdi_, Dec 10 2014
%e A177012 phi(15)=8 and 15^15 == -1 (mod 8), so 15 is in the sequence.
%t A177012 v={};Do[If[PowerMod[n,n,EulerPhi[n]]==EulerPhi[n]-1,AppendTo[v,n];
%t A177012 Print[v]],{n,200000000}]
%Y A177012 Cf. A000010, A177006.
%Y A177012 Cf. A050474, A203966.
%K A177012 nonn
%O A177012 1,2
%A A177012 _Farideh Firoozbakht_, May 19 2010
%E A177012 a(27)-a(29) from _Jahangeer Kholdi_, Dec 10 2014
%E A177012 a(30)-a(35) from _Farideh Firoozbakht_, Dec 10 2014