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 A292558 #24 Aug 28 2025 05:04:51
%S A292558 20,12,56,550,572,108,860,952,1232,6328,3708,40540,37072,79288,327260,
%T A292558 357112,302000,527296,1764056,6506512,38559776,21893248,42257216,
%U A292558 167771740,90798560,469761208,508198064,490304800,1353048560,2951488480,5067417200,32648918272,40086360272
%N A292558 a(n) is the smallest number k such that sigma(k) - 2k = 2^n.
%C A292558 For n > 31, a(n) > 1.724 * 10^10.
%C A292558 a(1) = A088831(1), a(2) = A088832(1), a(3) = A088833(1), a(4) = A141547(1), a(5) = A175989(1), a(6) = A275996(1), a(7) = A292626(1). - _Max Alekseyev_, Aug 27 2025
%H A292558 Max Alekseyev, <a href="/A292558/b292558.txt">Table of n, a(n) for n = 1..50</a>
%e A292558 sigma(20) - 2*20 = 2^1, a(1) = 20.
%e A292558 sigma(108) - 2*108 = 64 = 2^6, a(6) = 108.
%t A292558 Table[k = 1; While[Log[2, DivisorSigma[1, k] - 2k] != n, k++]; k, {n, 30}]
%o A292558 (PARI) a(n) = my(k=1); while(sigma(k) - 2*k != 2^n, k++); k; \\ _Michel Marcus_, Sep 19 2017
%Y A292558 Cf. A000203, A033880, A088831, A088832, A088833, A141547, A175989, A275996.
%K A292558 nonn,changed
%O A292558 1,1
%A A292558 _XU Pingya_, Sep 19 2017
%E A292558 Terms a(32) onward from _Max Alekseyev_, Aug 27 2025