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 A032619 #15 Aug 31 2021 20:11:42
%S A032619 3,5,17,27,35,39,45,47,63,65,83,93,99,113,123,147,149,173,185,203,209,
%T A032619 213,219,227,239,249,255,263,267,285,287,303,309,317,327,329,333,363,
%U A032619 365,399,413,419,423,435,447,459,465,467,473,489,497,509,515,519
%N A032619 Numbers k such that k concatenated with k+4 is a prime.
%H A032619 Robert Israel, <a href="/A032619/b032619.txt">Table of n, a(n) for n = 1..10000</a>
%p A032619 filter:= n -> isprime(n*(10^(1+ilog10(n+4))+1)+4):
%p A032619 select(filter, [seq(i,i=1..1000,2)]); # _Robert Israel_, Nov 14 2019
%t A032619 prkk4Q[k_]:=With[{c=k+4},PrimeQ[k*10^IntegerLength[c]+c]]; Select[ Range[ 600],prkk4Q] (* _Harvey P. Dale_, Aug 31 2021 *)
%Y A032619 Cf. A032609.
%K A032619 nonn,base
%O A032619 1,1
%A A032619 _Patrick De Geest_, May 15 1998