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 A126721 #20 Oct 30 2018 20:16:28
%S A126721 19333,20809,22573,25261,33247,38461,45013,48907,52321,60169,60961,
%T A126721 62233,62989,64333,64513,69499,73141,76039,83137,83497,84589,86029,
%U A126721 88129,88339,88681,90313,96097,97327,110989,113287,117577,121189,122611,125551,130729,131797,135937,137659,139201
%N A126721 Primes p such that q-p = 40, where q is the next prime after p.
%C A126721 From _Zak Seidov_: First terms followed by gaps 40, 2, 40: (383179, 1269601, 1528897, ...). First term followed by gaps 40, 2, 40, 2, 40 is 13504819. - _M. F. Hasler_, Oct 29 2018
%H A126721 Remi Eismann, <a href="/A126721/b126721.txt">Table of n, a(n) for n = 1..10000</a>
%H A126721 <a href="/index/Pri#gaps">Index entries for primes, gaps between</a>
%p A126721 a:=p->`if`(ithprime(p+1)-ithprime(p)=40,ithprime(p),NULL); seq(a(p),p=1..13000); # _Muniru A Asiru_, Oct 29 2018
%t A126721 Transpose[Select[Partition[Prime[Range[11000]],2,1],#[[2]]-#[[1]] == 40&]][[1]] (* _Harvey P. Dale_, Apr 18 2012 *)
%o A126721 (PARI) A(N=100,g=40,p=2,i=primepi(p)-1,L=[])={forprime(q=1+p,,i++; if(p+g==p=q, L=concat(L,q-g); N--||break));L} \\ returns the list of first N terms of the sequence. - _M. F. Hasler_, Oct 19 2018
%K A126721 nonn
%O A126721 1,1
%A A126721 _Rémi Eismann_, Feb 13 2007