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

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, 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, 0, 2, 2, 1, 3, 2, 2, 1, 0, 0, 2, 3, 0, 3, 0, 2, 2, 0

Offset: 1

Author

Colin Barker, Apr 10 2014

Keywords

• nonn
• base

Examples

			a(16) = 0 because prime(16) = 53, and 531, 533, 537 and 539 are not prime.
a(5) = 1 because prime(5) = 11, and 113 is prime, but 111, 117 and 119 are not prime.
a(1) = 2 because prime(1) = 2, and 23 and 29 are prime, but 21 and 27 are not prime.
a(4) = 3 because prime(4) = 7, and 71, 73 and 79 are prime, but 77 is not prime.
a(8) = 4 because prime(8) = 19, and 191, 193, 197 and 199 are all prime.
		

Links

• Colin Barker, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A067267, A119289, A240678, A240679, A240680.

Programs

Mathematica

Count[#,?PrimeQ]&/@Table[10*Prime[n]+k,{n,90},{k,{1,3,7,9}}] (* _Harvey P. Dale, Mar 25 2018 *)

PARI

forprime(p=2, 10000, t=0; forstep(k=1, 9, 2, if(isprime(p*10+k), t++)); print1(t, ", "))