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 A070286 #22 Dec 26 2024 03:53:46
%S A070286 1,4,7,8,12,14,15,24,28,32,39,42,56,60,63,72,80,84,90,91,96,104,112,
%T A070286 114,120,124,126,128,133,160,168,171,186,195,210,216,224,234,240,248,
%U A070286 252,255,256,260,280,288,294,300,308,312,336,360,363,372,378,384,392
%N A070286 Numbers k such that the equation sigma(sigma(x)) = k has solutions.
%C A070286 Complement of A162923. - _Jaroslav Krizek_, Jul 19 2009
%H A070286 Ivan Neretin, <a href="/A070286/b070286.txt">Table of n, a(n) for n = 1..10000</a>
%H A070286 Max Alekseyev, <a href="https://oeis.org/wiki/User:Max_Alekseyev/gpscripts">PARI/GP Scripts for Miscellaneous Math Problems</a> (invphi.gp).
%t A070286 mx = 400; Select[Union@Table[Nest[DivisorSigma[1, #] &, n, 2], {n, mx}], # < mx &] (* _Ivan Neretin_, Feb 12 2018 *)
%o A070286 (PARI) is(k) = {my(v = invsigma(k)); for(i = 1, #v, if(invsigmaNum(v[i]) > 0, return(1))); 0;} \\ _Amiram Eldar_, Dec 26 2024, using _Max Alekseyev_'s invphi.gp
%Y A070286 Cf. A051027, A162923.
%K A070286 easy,nonn
%O A070286 1,2
%A A070286 _Benoit Cloitre_, May 10 2002