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