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 A190821 #21 Oct 30 2015 10:15:51
%S A190821 7,19,41,199,919,5741,18089,41651,90271,446081,1276001,27033161,
%T A190821 43220449,53308529,109245401,512669249,663929729,2266639649,
%U A190821 2560742911,2969200961,8505402751,32540473601,61573368401,74335064959,109494811999
%N A190821 Prime numbers p where d(p-1) = d(p+1) increases to a record.
%C A190821 a(26) <= 354208192001. - _Donovan Johnson_, Jun 03 2011
%e A190821 a(1) = 7 because 7 is prime and d(6) = 4 = d(8).
%t A190821 s = Select[Prime@ Range@ 1000000, DivisorSigma[0, # - 1] == DivisorSigma[0, # + 1] &]; t = DivisorSigma[0, # - 1] & /@ s; a = {0}; b = {0}; Do[If[t[[k]] > Max@ b, AppendTo[a, s[[k]]]]; AppendTo[b, t[[k]]], {k, Length@ s}]; a (* _Michael De Vlieger_, Oct 30 2015 *)
%o A190821 (PARI) r=0; forprime(p=2,4e9,t=numdiv(p-1);if(t>r&t==numdiv(p+1),r=t; print1(p", "))) \\ _Charles R Greathouse IV_, May 27 2011
%Y A190821 Cf. A145337, A190646 (numbers n such that d(n-1)=d(n+1) increases to a record).
%K A190821 nonn
%O A190821 1,1
%A A190821 _Juri-Stepan Gerasimov_, May 21 2011
%E A190821 a(14)-a(21) from _Charles R Greathouse IV_, May 27 2011
%E A190821 a(22) from _Charles R Greathouse IV_, May 31 2011
%E A190821 a(23)-a(25) from _Donovan Johnson_, Jun 03 2011