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 A204878 #18 Feb 16 2025 08:33:16 %S A204878 1,2,3,4,5,7,8,9,10,11,13,14,15,16,17,19,20,21,22,23,25,26,27,29,31, %T A204878 32,33,35,37,38,39,41,43,44,45,47,49,50,51,53,55,57,59,61,63,65,67,69, %U A204878 71,73,75,77,79,81,83,85,87,89,91,93,95,97,99,101,103,105 %N A204878 Numbers that cannot be written as sum of perfect numbers. %C A204878 Complement of A204879; A097796(a(n)) = 0. %H A204878 Reinhard Zumkeller, <a href="/A204878/b204878.txt">Table of n, a(n) for n = 1..1000</a> %H A204878 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PerfectNumber.html">Perfect Number</a> %H A204878 Wikipedia, <a href="http://www.wikipedia.org/wiki/Perfect_number">Perfect number</a> %F A204878 a(38+k) = 49+2k for all k>0 (up to occurrence of an odd perfect number, known to be > 10^300, if it exists). - _M. F. Hasler_, Feb 09 2012 %o A204878 (Haskell) %o A204878 import Data.List (elemIndices) %o A204878 a204878 n = a204878_list !! (n-1) %o A204878 a204878_list = map (+ 1) $ elemIndices 0 a097796_list %Y A204878 Cf. A000396 (perfect numbers). %K A204878 nonn %O A204878 1,2 %A A204878 _Reinhard Zumkeller_, Jan 20 2012