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 A015863 #41 Feb 13 2025 19:19:44
%S A015863 51,66,115,220,319,1003,2585,4024,4183,4195,5720,5826,5959,8004,8374,
%T A015863 11659,12367,12561,13581,14338,15365,16116,17840,18718,20541,25130,
%U A015863 29393,30170,32665,36516,39913,40660,42423,42922,47841,49762
%N A015863 Numbers k such that sigma(k) = sigma(k+4).
%D A015863 J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 51, p. 19, Ellipses, Paris 2008.
%H A015863 Donovan Johnson, <a href="/A015863/b015863.txt">Table of n, a(n) for n = 1..1000</a> (first 130 terms from Paolo P. Lava)
%H A015863 A. Weingartner, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL14/Weingartner/wein3.html">On the Solutions of sigma(n) = sigma(n+k)</a>, Journal of Integer Sequences, Vol. 14 (2011), #11.5.5.
%t A015863 Select[Range[60000], DivisorSigma[1, #]==DivisorSigma[1, # + 4] &] (* _Vincenzo Librandi_, Mar 10 2014 *)
%t A015863 SequencePosition[DivisorSigma[1,Range[50000]],{x_,_,_,_,x_}][[;;,1]] (* _Harvey P. Dale_, Feb 13 2025 *)
%o A015863 (PARI) is(n)=sigma(n)==sigma(n+4) \\ _Charles R Greathouse IV_, Mar 09 2014
%Y A015863 Cf. A002961, A007373, A015861, A015865, A015866, A015867, A015876, A015877, A015880, A015881, A015882, A015883, A181647.
%K A015863 nonn
%O A015863 1,1
%A A015863 _Robert G. Wilson v_