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 A338504 #7 Oct 31 2020 13:54:12
%S A338504 0,0,1,0,2,0,3,0,0,0,4,0,5,0,0,0,6,0,7,0,0,0,8,0,1,1,0,0,9,0,10,0,1,0,
%T A338504 1,0,11,1,0,0,12,0,13,0,0,0,14,0,1,0,1,0,15,0,1,0,0,0,16,0,17,0,0,0,0,
%U A338504 0,18,0,0,0,19,0,20,1,0,1,1,0,21,0,2,0,22,0,1,1,1,0,23,0,2
%N A338504 Number of integers less than n with the same sum of proper divisors as n.
%F A338504 a(n) = |{j < n : sigma(j) - j = sigma(n) - n}|.
%e A338504 a(5) = 2 because A001065(5) = 1 and also A001065(2) = A001065(3) = 1.
%t A338504 Table[Length[Select[Range[n - 1], DivisorSigma[1, #] - # == DivisorSigma[1, n] - n &]], {n, 91}]
%o A338504 (PARI) a(n)={my(t=sigma(n)-n); sum(k=1, n-1, sigma(k)-k==t)} \\ _Andrew Howroyd_, Oct 31 2020
%Y A338504 Cf. A001065, A047983, A263025.
%K A338504 nonn
%O A338504 1,5
%A A338504 _Ilya Gutkovskiy_, Oct 31 2020