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 A136548 #47 Mar 28 2020 15:09:51
%S A136548 1,1,2,3,3,5,5,7,7,7,7,11,11,13,13,13,13,17,17,19,19,19,19,23,23,23,
%T A136548 23,23,23,29,29,31,31,31,31,31,31,37,37,37,37,41,41,43,43,43,43,47,47,
%U A136548 47,47,47,47,53,53,53,53,53,53,59,59,61,61,61,61,61,61,67,67,67,67,71,71
%N A136548 a(n) = max {k >= 1 | sigma(k) <= n}.
%C A136548 Old name was "Extended 'previous prime' version 2".
%C A136548 This is the same as A151799 if n >= 3 and falls back to 1, if no prime smaller than n exists.
%C A136548 a(n+1) is the largest number k such that A007955(k) <= n, where A007955 is the product of divisors. - _Jaroslav Krizek_, Apr 01 2010
%C A136548 For every k >= 1, the equation n - a(n) = k has infinitely many solutions. - _Bernard Schott_, Mar 05 2019
%D A136548 P. Tauvel, Exercices d'Algèbre Générale et d'Arithmétique, Dunod, 2004, Exercice 18 p. 204.
%H A136548 Enrique Pérez Herrero, <a href="/A136548/b136548.txt">Table of n, a(n) for n = 1..5000</a>
%F A136548 a(n) = A006530(A000142(n-1)). - _Michel Marcus_, Jun 20 2014
%F A136548 For n > 1, a(n) < n. If p is prime, a(p+1) = p. - _Bernard Schott_, Mar 05 2019
%t A136548 A136548[1]:= 1; A136548[2]:= 1; A136548[n_]:= Prime[PrimePi[n-1]]; Array[A136548,50] (* _Enrique Pérez Herrero_, Jul 23 2011 *)
%Y A136548 Cf. A000203 (sigma), A000142, A006530, A151799.
%K A136548 nonn,easy
%O A136548 1,3
%A A136548 _Roger L. Bagula_, Mar 26 2008
%E A136548 Definition clarified by _N. J. A. Sloane_, Mar 14 2019 based on a suggestion from _Jaroslav Krizek_, Mar 01 2010.