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 A015881 #28 Feb 10 2024 11:36:03 %S A015881 28,154,466,874,958,1054,2266,2878,11505,12754,14674,17974,21154, %T A015881 21778,29223,29535,31725,32714,39658,43186,48004,52018,62338,70198, %U A015881 126795,132783,163251,164818,207603,212938,221595,272685,274527 %N A015881 Numbers k such that sigma(k) = sigma(k+11). %H A015881 Donovan Johnson, <a href="/A015881/b015881.txt">Table of n, a(n) for n = 1..1000</a> %t A015881 Select[Range[300000], DivisorSigma[1, #]==DivisorSigma[1, # + 11] &] (* _Vincenzo Librandi_, Mar 10 2014 *) %t A015881 Position[Partition[DivisorSigma[1,Range[300000]],12,1],_?(First[#]== Last[#]&), 1,Heads->False]//Flatten (* _Harvey P. Dale_, Aug 20 2017 *) %o A015881 (PARI) is(n)=sigma(n)==sigma(n+11) \\ _Charles R Greathouse IV_, Mar 09 2014 %Y A015881 Cf. A002961, A007373, A015861, A015863, A015865, A015866, A015867, A015876, A015877, A015880, A015882, A015883, A181647. %K A015881 nonn %O A015881 1,1 %A A015881 _Robert G. Wilson v_