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 A077094 #27 May 07 2025 08:18:19
%S A077094 4,6,8,9,10,12,14,15,16,18,20,21,22,25,26,27,28,30,32,33,34,35,38,39,
%T A077094 44,45,46,49,51,54,55,56,57,58,62,63,65,68,70,77,85,87,91,93,95,99,
%U A077094 104,111,119,121,129,134,143,145,153,158,161,169,189,205,209,215,221,245
%N A077094 Numbers k such that iterating phi(sigma(k)-phi(k)) starting from k leads to the fixed point 4.
%C A077094 Probably this sequence is finite, with 92 terms of which the last is 6241.
%H A077094 Sean A. Irvine, <a href="/A077094/b077094.txt">Table of n, a(n) for n = 1..92</a>
%e A077094 n=6241: FixedPointList={6241,104,54,32,20,16,22,12,8,10,6,4}, end=4.
%t A077094 f[x_] := EulerPhi[DivisorSigma[1, x]-EulerPhi[x]]; Do[s=NestList[f, n, 100]; s1=Part[s, 99]; s2=Part[s, 100]; If[Equal[s1, s2]&&Equal[s1, 4], Print[{n, s1}]], {n, 1, 1000000}]
%t A077094 f4[n_]:=FixedPoint[EulerPhi[DivisorSigma[1,#]-EulerPhi[#]]&,n,50]==4; Select[Range[250],f4] (* _Harvey P. Dale_, May 01 2021 *)
%Y A077094 Cf. A000010 (phi), A000203 (sigma).
%Y A077094 Cf. A077090, A077091, A077092, A077093, A077095, A077096.
%K A077094 nonn
%O A077094 1,1
%A A077094 _Labos Elemer_, Oct 31 2002
%E A077094 Definition corrected by _Harvey P. Dale_, May 01 2021