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 A171056 #11 Mar 31 2017 00:44:18
%S A171056 2,3,5,9,11,13,19,17,23,27,31,39,41,43,49,53,57,61,69,91,93,97,83,87,
%T A171056 79,101,103,109,107,113,129,131,139,137,147,151,159,163,169,193,197,
%U A171056 181,171,173,179,177,211,223,229,227,233,237,241,251,259,263
%N A171056 In the sequence of prime numbers, replace all the '9' digits with '7' and vice versa.
%H A171056 Vincenzo Librandi, <a href="/A171056/b171056.txt">Table of n, a(n) for n = 1..1000</a>
%t A171056 FromDigits[IntegerDigits[#] /. {9 -> p, 7 -> q} /. {p -> 7, q -> 9}] & /@ Prime[Range[100]] (* _Vincenzo Librandi_, Apr 07 2013 *)
%o A171056 (PARI) a(n)=my(v=[0,1,2,3,4,5,6,9,8,7]);subst(Pol(apply(k->v[k+1], digits(prime(n)))),'x,10) \\ _Charles R Greathouse IV_, Jul 31 2013
%K A171056 nonn,base,easy
%O A171056 1,1
%A A171056 _N. J. A. Sloane_ and _Vincenzo Librandi_, Sep 04 2010