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 A189828 #12 Jul 15 2025 10:52:03
%S A189828 2,3,5,7,11,17,19,29,41,71,161,169,181,239,419,701,721,881,1079,1681,
%T A189828 2159,2519,2521,4031,4159,5039,7561,8399,10081,13441,13859,18721,
%U A189828 20161,22679,25199,27719,27721,35281,45361,50399,50401,55439,65519,110879,138599
%N A189828 Numbers k for which d(k-1) + d(k+1) is a record, where d(k) is the number of divisors of k.
%C A189828 Many of these terms are in A090481, which restricts k to be prime. The record values are in A189829.
%H A189828 Donovan Johnson, <a href="/A189828/b189828.txt">Table of n, a(n) for n = 1..135</a>
%t A189828 DeleteDuplicates[Table[{n,DivisorSigma[0,n-1]+DivisorSigma[0,n+1]},{n,2,140000}],GreaterEqual[#1[[2]],#2[[2]]]&][[;;,1]] (* _Harvey P. Dale_, Jul 14 2025 *)
%Y A189828 Cf. A090481, A189827, A189829.
%K A189828 nonn
%O A189828 1,1
%A A189828 _T. D. Noe_, Apr 28 2011