A036946 - OEIS

%I #16 Mar 09 2020 09:12:00

%S 5,0,557,5557,57557,555557,5555777,55555777,555557557,5555555557,

%T 55555555777,555555575557,5555555757757,55555555575757,

%U 555555555555557,5555555555557577,55555555555777777,555555555557557757,5555555555555557577,55555555555575755777

%N Smallest n-digit prime containing only the digits 5 and 7, or 0 if no such prime exists.

%H Jinyuan Wang, <a href="/A036946/b036946.txt">Table of n, a(n) for n = 1..500</a>

%t Flatten[Join[{5,0},Table[Select[FromDigits/@(Join[#,{7}]&/@Tuples[ {5,7},n]), PrimeQ,1],{n,2,20}]]] (* _Harvey P. Dale_, Mar 08 2013 *)

%Y Cf. A020467, A036229, A036320.

%K nonn,base

%O 1,1

%A _Patrick De Geest_, Jan 04 1999

%E More terms from _Harvey P. Dale_, Mar 08 2013