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 A274793 #23 Apr 20 2023 04:22:05
%S A274793 2,3,5,7,9,10,11,15,16,17,19,21,22,23,25,26,27,28,29,33,34,35,36,37,
%T A274793 39,41,43,45,46,47,49,50,51,52,53,55,58,59,61,63,64,65,66,67,69,70,71,
%U A274793 73,75,76,77,79,81,82,83,85,86,87,88,89,91,92,93,94,95,97,99,100
%N A274793 Numbers not in the range of the sum of odd divisors function.
%C A274793 Numbers which do not appear in A000593; that is, there is no positive integer N whose sum of odd divisors is equal to a(n) for any n.
%C A274793 The sum of odd divisors of x is equal to sigma(x) if and only if x is odd. So, there are numbers in the range of sigma(x) that are not in the range of the sum of odd divisors function.
%H A274793 Amiram Eldar, <a href="/A274793/b274793.txt">Table of n, a(n) for n = 1..10000</a>
%t A274793 TakeWhile[Complement[Range@ #, Union@ Table[Total@ Select[Divisors@ n, OddQ], {n, 2 #}]], Function[k, k <= #]] &@ 100 (* _Michael De Vlieger_, Jul 07 2016 *)
%Y A274793 Cf. A000593, supersequence of A007369, A274790 (complement).
%K A274793 nonn
%O A274793 1,1
%A A274793 _Timothy L. Tiffin_, Jul 07 2016