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 A090152 #7 Apr 23 2019 18:34:33
%S A090152 41,43,47,433,499,4111,4999,47777,49999,4999999,41111111111111,
%T A090152 47777777777777,499999999999999,43333333333333333,
%U A090152 41111111111111111111111111,47777777777777777777777777
%N A090152 Primes of the form identical digits preceded by a 4.
%H A090152 Vincenzo Librandi, <a href="/A090152/b090152.txt">Table of n, a(n) for n = 1..36</a>
%t A090152 Select[ FromDigits /@ Flatten[ Table[ PadRight[{4}, i, # ] & /@ {1, 2, 3, 4, 5, 6, 7, 8, 9}, {i, 2, 24}], 1], PrimeQ[ # ] &]
%t A090152 Select[Flatten[Table[FromDigits[PadRight[{4},n,k]],{n,2,30},{k,{1,3,7,9}}]],PrimeQ] (* _Harvey P. Dale_, Apr 23 2019 *)
%K A090152 nonn,base
%O A090152 1,1
%A A090152 _Robert G. Wilson v_, Nov 22 2003