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 A171038 #12 Mar 31 2017 11:09:12
%S A171038 2,3,5,4,11,13,14,19,23,29,31,34,71,73,74,53,59,61,64,41,43,49,83,89,
%T A171038 94,101,103,104,109,113,124,131,134,139,179,151,154,163,164,143,149,
%U A171038 181,191,193,194,199,211,223,224,229,233,239,271,251,254,263
%N A171038 In the sequence of prime numbers, replace all the '7' digits with '4' and vice versa.
%H A171038 Vincenzo Librandi, <a href="/A171038/b171038.txt">Table of n, a(n) for n = 1..1000</a>
%t A171038 fixp[n_]:=FromDigits[IntegerDigits[n]/.{7->a,4->b}/.{a->4,b->7}]; fixp/@Prime[Range[100]] (* _Harvey P. Dale_, Apr 25 2011 *)
%o A171038 (PARI) a(n)=my(v=[0,1,2,3,7,5,6,4,8,9]);subst(Pol(apply(k->v[k+1], digits(prime(n)))),'x,10) \\ _Charles R Greathouse IV_, Jul 25 2013
%K A171038 nonn,base,easy
%O A171038 1,1
%A A171038 _N. J. A. Sloane_ and _Vincenzo Librandi_, Sep 04 2010