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%I #10 Jul 22 2021 02:11:53
%S 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 71,73,77,79,83,89,95,97,99,101,103,107,109,113,115,119,125,127,131,
%U 135,137,139,141,147,149,151,155,157,163,167,171,173,179,181,191,193,197,199,207,211,215,219
%N Numbers k such that A111273(k-1) = k.
%C All terms are odd; includes all odd primes.
%C 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 Robert Israel, <a href="/A309203/b309203.txt">Table of n, a(n) for n = 1..10000</a>
%p S:= {}:
%p R:= NULL: count:= 0:
%p for n from 1 while count < 200 do
%p v:= min(numtheory:-divisors(n*(n+1)/2) minus S);
%p S:= S union {v};
%p if v = n+1 then R:= R, n+1; count:= count+1 fi;
%p od:
%p R; # _Robert Israel_, Jul 30 2019
%Y Cf. A111273.
%K nonn
%O 1,1
%A _N. J. A. Sloane_, Jul 27 2019
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