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 A154531 #14 Feb 20 2017 12:15:50
%S A154531 199211,211199,233239,239233,257263,263257,353359,359353,523541,
%T A154531 541523,653659,659653,971977,977971,19731979,19791973,23332339,
%U A154531 23392333,32593271,32713259,36373643,36433637,37613767,37673761,42834289,42894283,49934999,49994993
%N A154531 Primes that are a concatenation of consecutive primes in two ways.
%H A154531 Harvey P. Dale, <a href="/A154531/b154531.txt">Table of n, a(n) for n = 1..1000</a>
%e A154531 233 and 239 consecutive primes, 233239 and 239233 are both primes.
%t A154531 ccp2[{a_,b_}]:=Module[{c=a*10^IntegerLength[b]+b,d=b*10^IntegerLength[a]+ a}, If[ AllTrue[ {c,d}, PrimeQ],{c,d},{}]]; ccp2/@Partition[Prime[ Range[ 1000]],2,1]//Flatten (* The program uses the AllTrue function from Mathematica version 10 *) (* _Harvey P. Dale_, Feb 20 2017 *)
%Y A154531 Cf. A133986, A154530.
%K A154531 nonn,base
%O A154531 1,1
%A A154531 _Pierre CAMI_, Jan 11 2009
%E A154531 Corrected by _Harvey P. Dale_, Feb 20 2017