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%I A228325 #20 Oct 18 2022 10:45:23
%S A228325 3,3,7,7,9,7,9,9,11,13,17,13,19,23,23,19,21,23,31,27,29,37,33,37,31,
%T A228325 33,29,33,39,37,37,51,43,49,39,37,39,47,43,49,53,43,49,47,47,49,51,61,
%U A228325 51,51,53,61,81,71,57,57,79,61,81,67,63,63,67,69,69,73,79
%N A228325 a(n) is the smallest number m>n such that the concatenation nm is prime.
%C A228325 Max Alekseyev (see link in A068695) shows that a(n) always exists. - _N. J. A. Sloane_, Nov 13 2020
%C A228325 Suggested by the existence question in A228323.
%H A228325 Paul Tek, <a href="/A228325/b228325.txt">Table of n, a(n) for n = 1..10000</a>
%H A228325 <a href="/index/Pri#piden">Index entries for primes involving decimal expansion of n</a>
%e A228325 12 is not prime but 13 is, so a(1)=3.
%e A228325 23 is prime so a(2)=3.
%e A228325 34, 35, 36 are not prime but 37 is, so a(3)=7.
%t A228325 smc[n_]:=Module[{m=n+1},If[OddQ[n],m++];While[!PrimeQ[n*10^IntegerLength[ m]+ m],m=m+2];m]; Array[smc,70] (* _Harvey P. Dale_, Apr 30 2016 *)
%o A228325 (Python)
%o A228325 from sympy import isprime
%o A228325 from itertools import count
%o A228325 def a(n): return next(k for k in count(n+1) if isprime(int(str(n)+str(k))))
%o A228325 print([a(n) for n in range(1, 68)]) # _Michael S. Branicky_, Oct 18 2022
%Y A228325 Cf. A228323, A068695.
%K A228325 nonn,base
%O A228325 1,1
%A A228325 _N. J. A. Sloane_, Aug 20 2013

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