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A036941 Smallest n-digit prime containing only digits 3 and 5, or 0 if no such prime exists.

%I A036941 #18 Oct 10 2019 23:00:53
%S A036941 3,53,353,3533,33353,333533,3335533,33335333,333535333,3333353533,
%T A036941 33333353533,333333533353,3333333353353,33333333555553,
%U A036941 333333333353353,3333333333333533,33333333333355333,333333333333353533
%N A036941 Smallest n-digit prime containing only digits 3 and 5, or 0 if no such prime exists.
%H A036941 Robert Israel, <a href="/A036941/b036941.txt">Table of n, a(n) for n = 1..990</a>
%p A036941 A:= proc(n) local j,x,t;
%p A036941   x:= (10^n-1)/3;
%p A036941   for t from 1 to 2^n do
%p A036941     if isprime(x) then return x fi;
%p A036941     j:= padic:-ordp(t,2);
%p A036941     x:= x  - (x mod 10^j) + (7 * 10^j-1)/3;
%p A036941   od:
%p A036941   0
%p A036941 end proc:
%p A036941 seq(A(n),n=1..100); # _Robert Israel_, Apr 22 2016
%t A036941 Table[SelectFirst[FromDigits/@(Join[#,{3}]&/@Tuples[{3,5},n]),PrimeQ],{n,0,20}](* The program uses the SelectFirst function from Mathematica version 10 *) (* _Harvey P. Dale_, Oct 07 2014 *)
%Y A036941 Cf. A036229, A020462, A036315.
%K A036941 nonn,base
%O A036941 1,1
%A A036941 _Patrick De Geest_, Jan 04 1999