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 A206036 #23 Dec 16 2024 02:01:53
%S A206036 6,10,11,14,15,16,17,20,21,23,24,25,26,28,30,31,33,34,35,38,39,40,41,
%T A206036 42,44,46,47,48,51,52,53,54,55,56,57,58,59,60,62,63,65,66,68,69,70,71,
%U A206036 74,75,76,77,78,79,80,82,83,84,85,86,87,88,89,90,92,93,94
%N A206036 Numbers m such that sigma(m) = sigma(k) has solution for distinct numbers m and k.
%H A206036 Amiram Eldar, <a href="/A206036/b206036.txt">Table of n, a(n) for n = 1..10000</a>
%H A206036 Max Alekseyev, <a href="https://oeis.org/wiki/User:Max_Alekseyev/gpscripts">PARI/GP Scripts for Miscellaneous Math Problems</a> (invphi.gp).
%e A206036 6 and 11 are in the sequence because sigma(6) = sigma(11) = 12.
%e A206036 7 is not on the list because sigma(7) = 8 and there is no other integer for which sigma(n) = 8.
%t A206036 max = 9000; sigmaList = Table[DivisorSigma[1, n], {n, Prime[PrimePi[max]]}]; Select[Range[Floor[Sqrt[max]]], Count[sigmaList, sigmaList[[#]]] > 1 &] (* _Alonso del Arte_, Feb 06 2012 *)
%o A206036 (PARI) is(k) = invsigmaNum(sigma(k)) > 1; \\ _Amiram Eldar_, Dec 15 2024, using _Max Alekseyev_'s invphi.gp
%Y A206036 Complement of A211656.
%Y A206036 Cf. A000203, A054973, A066074, A158913.
%K A206036 nonn
%O A206036 1,1
%A A206036 _Jaroslav Krizek_, Feb 03 2012