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A373859 Smallest prime obtained by appending one or more 9's to n, -1 if no such prime exists.

%I A373859 #18 Jul 08 2024 19:25:40
%S A373859 19,29,-1,499,59,-1,79,89,-1,109,1199999,-1,139,149,-1,1699,179,-1,
%T A373859 199,2099,-1,229,239,-1,25999,269,-1,289999,2999,-1,
%U A373859 319999999999999999999999999999,3299,-1,349,359,-1,379,389,-1,409,419,-1,439,449,-1
%N A373859 Smallest prime obtained by appending one or more 9's to n, -1 if no such prime exists.
%H A373859 Toshitaka Suzuki, <a href="/A373859/b373859.txt">Table of n, a(n) for n = 1..448</a>
%F A373859 a(11) = 1199999 because 119, 1199, 11999 and 119999 are not primes.
%o A373859 (Python)
%o A373859 from itertools import count
%o A373859 from sympy import isprime
%o A373859 def A373859(n): return next(p for p in ((n+1)*10**m-1 for m in count(1)) if isprime(p)) if n%3 else -1 # _Chai Wah Wu_, Jul 08 2024
%Y A373859 Cf. A030433, A373201, A112386, A372056, A113076.
%K A373859 base,sign
%O A373859 1,1
%A A373859 _Toshitaka Suzuki_, Jun 19 2024