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A088115 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. 0

%I

%S 0,2,3,31,5,0,7,71,0,73,83,0,67,59,0,97,89,0,991,983,0,967,977,0,997,

%T 9791,0,9973,9929,0,9967,9887,0,99961,8999,0,99991,99929,0,99877,

%U 99689,0,98899,99989,0,999883,999983,0,999769,999959,0,999979,989999,0

%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.

%K base,nonn

%O 1,2

%A _Amarnath Murthy_, Sep 25 2003

%E More terms from _David Wasserman_, Jul 25 2005

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Last modified July 17 20:45 EDT 2019. Contains 325109 sequences. (Running on oeis4.)