%I

%S 1,3,1,1,3,1,1,147,17,1,3,7,1,297,1

%N Smallest k>0 such that n*10^k + k is prime.

%C (a(n) mod 10) in {1,3,7,9}.

%C a(16), if it exists, is greater than 20000. - _Ryan Propper_, Jul 21 2006

%C a(16), if it exists, is greater than 42000. - _Ryan Propper_, Sep 25 2006

%Y a(floor(A030430(n)/10)) = 1.

%K nonn,more

%O 1,2

%A _Reinhard Zumkeller_, Mar 07 2005