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 A309203 #10 Jul 22 2021 02:11:53
%S A309203 3,5,7,11,13,17,19,23,27,29,31,35,37,39,41,43,45,47,53,55,59,61,63,67,
%T A309203 71,73,77,79,83,89,95,97,99,101,103,107,109,113,115,119,125,127,131,
%U A309203 135,137,139,141,147,149,151,155,157,163,167,171,173,179,181,191,193,197,199,207,211,215,219
%N A309203 Numbers k such that A111273(k-1) = k.
%C A309203 All terms are odd; includes all odd primes.
%C A309203 The odd terms that are not primes are 27, 35, 39, 45, 55, 63, 77, 95, 99, 115, 119, 125, 135, 141, 147, 155, 171, .... What are these numbers?
%H A309203 Robert Israel, <a href="/A309203/b309203.txt">Table of n, a(n) for n = 1..10000</a>
%p A309203 S:= {}:
%p A309203 R:= NULL: count:= 0:
%p A309203 for n from 1 while count < 200 do
%p A309203 v:= min(numtheory:-divisors(n*(n+1)/2) minus S);
%p A309203 S:= S union {v};
%p A309203 if v = n+1 then R:= R, n+1; count:= count+1 fi;
%p A309203 od:
%p A309203 R; # _Robert Israel_, Jul 30 2019
%Y A309203 Cf. A111273.
%K A309203 nonn
%O A309203 1,1
%A A309203 _N. J. A. Sloane_, Jul 27 2019