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 A020471 #21 Jul 08 2025 01:40:58
%S A020471 7,79,97,797,977,997,77797,77977,77999,79777,79979,79997,79999,97777,
%T A020471 777977,777979,779797,797977,799979,799999,999979,7777997,7779979,
%U A020471 7779997,7797799,7797997,7799797,7799999,7977779,7977797,7977799,7977997
%N A020471 Primes that contain digits 7 and 9 only.
%H A020471 Jason Bard, <a href="/A020471/b020471.txt">Table of n, a(n) for n = 1..10000</a> (first 1000 terms from Vincenzo Librandi)
%H A020471 <a href="/index/Pri#PrimesWithDigits">Index to entries about primes with digits in a given set</a>
%t A020471 Flatten[Table[Select[FromDigits/@Tuples[{7,9},n],PrimeQ],{n,7}]] (* _Vincenzo Librandi_, Jul 28 2012 *)
%o A020471 (Magma) [p: p in PrimesUpTo(7977997) | Set(Intseq(p)) subset [7,9]]; // _Vincenzo Librandi_, Jul 28 2012
%Y A020471 Subsequence of A030096.
%Y A020471 Cf. A020449 (digits 0 & 1), ..., A020472 (digits 8 & 9).
%K A020471 nonn,base
%O A020471 1,1
%A A020471 _David W. Wilson_
%E A020471 Edited by _M. F. Hasler_, Jul 26 2015