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A240689 The number of values of the digit k for which prime(n)*10+k is prime.

%I A240689 #9 Mar 25 2018 09:39:26
%S A240689 2,2,2,3,1,3,2,4,2,1,3,2,1,3,1,0,2,3,2,1,2,1,1,0,2,2,3,0,3,0,2,1,1,1,
%T A240689 2,1,2,1,0,1,0,1,1,2,2,3,2,2,1,2,2,2,2,0,1,1,2,3,1,1,2,1,1,1,1,0,2,2,
%U A240689 0,2,2,1,3,2,2,1,0,0,2,3,0,3,0,2,2,0
%N A240689 The number of values of the digit k for which prime(n)*10+k is prime.
%H A240689 Colin Barker, <a href="/A240689/b240689.txt">Table of n, a(n) for n = 1..10000</a>
%e A240689 a(16) = 0 because prime(16) = 53, and 531, 533, 537 and 539 are not prime.
%e A240689 a(5) = 1 because prime(5) = 11, and 113 is prime, but 111, 117 and 119 are not prime.
%e A240689 a(1) = 2 because prime(1) = 2, and 23 and 29 are prime, but 21 and 27 are not prime.
%e A240689 a(4) = 3 because prime(4) = 7, and 71, 73 and 79 are prime, but 77 is not prime.
%e A240689 a(8) = 4 because prime(8) = 19, and 191, 193, 197 and 199 are all prime.
%t A240689 Count[#,_?PrimeQ]&/@Table[10*Prime[n]+k,{n,90},{k,{1,3,7,9}}] (* _Harvey P. Dale_, Mar 25 2018 *)
%o A240689 (PARI) forprime(p=2, 10000, t=0; forstep(k=1, 9, 2, if(isprime(p*10+k), t++)); print1(t, ", "))
%Y A240689 Cf. A067267, A119289, A240678, A240679, A240680.
%K A240689 nonn,base
%O A240689 1,1
%A A240689 _Colin Barker_, Apr 10 2014