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 A032721 #16 Aug 13 2024 11:14:04
%S A032721 5,6,8,12,15,17,21,29,32,33,35,39,44,45,50,51,54,56,59,63,65,78,81,87,
%T A032721 93,95,96,98,101,104,105,107,111,117,122,125,135,138,146,150,159,161,
%U A032721 162,164,168,173,177,188,189,192,194,195,201,215,218,219,222,225
%N A032721 Numbers k such that k prefixed by '4' and followed by '7' is prime.
%H A032721 Harvey P. Dale, <a href="/A032721/b032721.txt">Table of n, a(n) for n = 1..1000</a>
%t A032721 Select[Range[300],PrimeQ[FromDigits[Join[{4},IntegerDigits[#],{7}]]]&] (* _Harvey P. Dale_, Jan 08 2019 *)
%Y A032721 Cf. A032702-A032733.
%K A032721 nonn,base
%O A032721 1,1
%A A032721 _Patrick De Geest_, May 15 1998
%E A032721 Offset changed by _Andrew Howroyd_, Aug 13 2024