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Number of n-digit primes whose reversal is a different prime.
2

%I #12 Jun 28 2021 10:49:40

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

%T 2294771254

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

%C All terms are even.

%e a(1)=0 because there are no 1-digit terms in A006567.

%e a(2)=8 because there are eight 2-digit terms in A006567: 13,17,31,37,71,73,79,97.

%t 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}];

%Y Cf. A006567.

%K more,nonn,base

%O 1,2

%A _Zak Seidov_, Nov 19 2008

%E a(10)-a(11) from _Donovan Johnson_, Nov 01 2010

%E a(12) from _Lars Blomberg_, Jun 28 2021