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 A020466 #20 Sep 23 2020 03:27:46
%S A020466 449,499,4999,9949,44449,49499,49999,94949,94999,444449,994949,999499,
%T A020466 4444949,4449449,4944949,4949449,4999949,4999999,9444949,9494999,
%U A020466 9944449,9994499,44444999,44499449,44944499,44994949,49444949,49444999,49494499
%N A020466 Primes that contain digits 4 and 9 only.
%H A020466 Alois P. Heinz, <a href="/A020466/b020466.txt">Table of n, a(n) for n = 1..20000</a> (first 1000 terms from Vincenzo Librandi)
%H A020466 James Maynard and Brady Haran, <a href="https://www.youtube.com/watch?v=eeoBCS7IEqs">Primes without a 7</a>, Numberphile video (2019)
%t A020466 Flatten[Table[Select[FromDigits/@Tuples[{4,9},n],PrimeQ],{n,8}]] (* _Vincenzo Librandi_, Jul 27 2012 *)
%o A020466 (PARI) is(N)=isprime(N)&&!#setminus(Set(digits(N)), [4,9]) \\ _M. F. Hasler_, Sep 22 2020
%Y A020466 Cf. A036319 (composite numbers having all their prime factors in this sequence).
%K A020466 nonn,base
%O A020466 1,1
%A A020466 _David W. Wilson_