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 A088283 #7 Jun 15 2015 11:18:25
%S A088283 727,757,787,797,77377,77477,77977,7772777,7774777,7778777,777767777,
%T A088283 77777677777,7777774777777,777777727777777,777777757777777,
%U A088283 77777777677777777,77777777977777777,777777777727777777777
%N A088283 Palindromic primes in which a single digit is sandwiched between strings of 7's.
%H A088283 Harvey P. Dale, <a href="/A088283/b088283.txt">Table of n, a(n) for n = 1..37</a>
%t A088283 Select[Flatten[Table[FromDigits[Flatten[Join[{PadRight[{},n,7], i, PadRight[ {},n,7]}]]],{n,10},{i,0,9}]],PrimeQ] (* _Harvey P. Dale_, Jun 15 2015 *)
%Y A088283 Cf. A088281, A088282, A088284.
%K A088283 base,nonn
%O A088283 1,1
%A A088283 _Amarnath Murthy_, Sep 29 2003
%E A088283 More terms from _David Wasserman_, Aug 03 2005