A152014 Number of n-digit primes whose reversal is a different prime.

0, 8, 28, 204, 1406, 9538, 70474, 535578, 4192024, 33619380, 274890230, 2294771254

Offset: 1

Author

Zak Seidov, Nov 19 2008

Keywords

• more
• nonn
• base

Comments

All terms are even.

Examples

			a(1)=0 because there are no 1-digit terms in A006567.
a(2)=8 because there are eight 2-digit terms in A006567: 13,17,31,37,71,73,79,97.
		

Crossrefs

Cf. A006567.

Programs

Mathematica

Do[c = 0; p = NextPrime[10^(n - 1) - 1]; n1 = PrimePi[p]; n2 = PrimePi[NextPrime[10^n, -1]] - n1 + 1; Do[id = IntegerDigits[p]; i1 = id[[1]]; If[OddQ[i1] && i1 != 5, p1 = FromDigits[ Reverse[id]]; If[p1 != p, If[PrimeQ[p1], c++ ]]]; p = NextPrime[p], {n2}]; Print[{n, c}], {n, 1, 9}];

Extensions

a(10)-a(11) from Donovan Johnson, Nov 01 2010

a(12) from Lars Blomberg, Jun 28 2021