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 A020469 #15 Nov 15 2022 10:46:54
%S A020469 7,67,677,67777,76667,76777,666667,677767,767677,777677,6676667,
%T A020469 6676777,6677677,6677767,6677777,6766667,6766777,6776677,7666667,
%U A020469 7667677,7667767,7766767,7766777,7777667,66666667,66677777,66776777,67667777,67766767,67776677,67776767
%N A020469 Primes that contain digits 6 and 7 only.
%H A020469 Michael S. Branicky, <a href="/A020469/b020469.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from Vincenzo Librandi)
%t A020469 Flatten[Table[Select[FromDigits/@Tuples[{6,7},n],PrimeQ],{n,8}]] (* _Vincenzo Librandi_, Jul 27 2012 *)
%o A020469 (Python)
%o A020469 from sympy import isprime
%o A020469 from itertools import count, islice, product
%o A020469 def agen(): # generator of terms
%o A020469 yield 7
%o A020469 for d in count(2):
%o A020469 for first in product("67", repeat=d-1):
%o A020469 t = int("".join(first) + "7")
%o A020469 if isprime(t): yield t
%o A020469 print(list(islice(agen(), 31))) # _Michael S. Branicky_, Nov 15 2022
%Y A020469 Cf. A020449-A020472.
%K A020469 nonn,base
%O A020469 1,1
%A A020469 _David W. Wilson_