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 A069688 #8 Mar 17 2015 23:12:37
%S A069688 5,7,31,37,41,43,53,59,61,67,73,79,83,101,103,139,151,157,179,197,223,
%T A069688 241,257,263,269,271,283,293,307,311,349,353,389,421,431,461,467,491,
%U A069688 557,593,599,601,607,631,643,647,683,691,701,727,757,769,811,827,839
%N A069688 Primes that yield another prime on placing a 3 on both sides (as leading and trailing digits).
%H A069688 Harvey P. Dale, <a href="/A069688/b069688.txt">Table of n, a(n) for n = 1..10000</a>
%e A069688 139 is a member as 31393 is also a prime.
%t A069688 Select[ Range[1000], PrimeQ[ # ] && PrimeQ[ FromDigits[ Insert[ IntegerDigits[ # ], 3, {{1}, {-1}}]]] &]
%t A069688 Select[Prime[Range[200]],PrimeQ[FromDigits[Join[{3},IntegerDigits[#],{3}]]]&] (* _Harvey P. Dale_, Oct 24 2011 *)
%Y A069688 Cf. A069687, A069689, A069690.
%K A069688 nonn,base
%O A069688 1,1
%A A069688 _Amarnath Murthy_, Apr 06 2002
%E A069688 Edited and extended by _Robert G. Wilson v_, May 03 2002