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 A087533 #15 Sep 20 2024 23:54:44
%S A087533 47,47447747,77474447,4447747747,4744477747,4744747477,4744747747,
%T A087533 4747444777,4747747447,4774744477,4774747447,7444477477,7447474477,
%U A087533 7744744747,7744747447,7747444477,7747447447,7747744447,44444477777477,44447447774777,44447474777477
%N A087533 Primes consisting only of digits 4 and 7 occurring with equal frequency.
%C A087533 There are 18 digit pairs which can produce such primes. (1,0),(1,3),(1,4),(1,6),(1,7),(1,9),(2,3),(2,9),(3,4),(3,5),(3,7),(3,8),(4,7),(4,9),(5,9),(6,7),(7,9),(8,9).
%H A087533 Harvey P. Dale, <a href="/A087533/b087533.txt">Table of n, a(n) for n = 1..10000</a>
%t A087533 Table[Select[FromDigits/@Permutations[PadRight[{},2n,{4,7}]],PrimeQ],{n,7}]//Flatten//Sort (* _Harvey P. Dale_, May 05 2016 *)
%o A087533 (PARI) \\ Needs B() from A087510.
%o A087533 concat(vector(6,k,B(k,4,7,isprime))) \\ _Andrew Howroyd_, Sep 20 2024
%Y A087533 Cf. A087510, A087511, A087532.
%K A087533 base,nonn
%O A087533 1,1
%A A087533 _Paul D. Hanna_ and _Amarnath Murthy_, Sep 12 2003
%E A087533 Edited by _Charles R Greathouse IV_, Oct 28 2009
%E A087533 Corrected by _Harvey P. Dale_, May 05 2016
%E A087533 Offset changed by _Andrew Howroyd_, Sep 20 2024