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 A272978 #24 Jul 14 2016 00:19:14 %S A272978 1,2,3,4,5,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26, %T A272978 27,29,30,31,32,33,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51, %U A272978 52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80 %N A272978 Numbers not in the range of the sum of perfect divisors function. %C A272978 Numbers which do not appear in A185351 or A187794; that is, there is no integer N whose sum of perfect divisors is equal to a(n) for any n. %Y A272978 Cf. A000396, subsequence of A132999, A185351 (complement), A187794. %K A272978 nonn %O A272978 1,2 %A A272978 _Timothy L. Tiffin_, Jul 13 2016