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 A171027 #9 Mar 31 2017 20:26:58
%S A171027 2,3,4,7,11,13,17,19,23,29,31,37,51,53,57,43,49,61,67,71,73,79,83,89,
%T A171027 97,101,103,107,109,113,127,131,137,139,159,141,147,163,167,173,179,
%U A171027 181,191,193,197,199,211,223,227,229,233,239,251,241,247,263
%N A171027 In the sequence of prime numbers, replace all the '5' digits with '4' and vice versa.
%H A171027 Vincenzo Librandi, <a href="/A171027/b171027.txt">Table of n, a(n) for n = 1..1000</a>
%t A171027 FromDigits[IntegerDigits[#]/.{5->p, 4->q}/.{p->4, q->5}]&/@Prime[Range[100]] (* _Vincenzo Librandi_, Apr 07 2013 *)
%o A171027 (PARI) a(n)=my(v=[0,1,2,3,5,4,6,7,8,9]);subst(Pol(apply(k->v[k+1], digits(prime(n)))),'x,10) \\ _Charles R Greathouse IV_, Jul 24 2013
%K A171027 nonn,base,easy
%O A171027 1,1
%A A171027 _N. J. A. Sloane_ and _Vincenzo Librandi_, Sep 04 2010