%N a(n) = largest prime using least number of possible digits with a digit sum n, or 0 if no such number exists. E.g., if n > 9 and there are no two-digit primes with a given digit sum n then three-digit numbers are explored and so on.
%C a(26) = 9719 as both 989 and 899 are composite. This is the first genuine case in which the number of digits used is more than floor(n/9) + 1 (after single-digit composite even numbers 4 and 8).
%e a(7) = 7.
%e a(8) = 71 as 8 is not a prime.
%A _Amarnath Murthy_, Sep 25 2003
%E More terms from _David Wasserman_, Jul 25 2005