A127746 Smallest n-digit prime whose reversal is also prime.

2, 13, 107, 1009, 10007, 100049, 1000033, 10000169, 100000007, 1000000007, 10000000207, 100000000237, 1000000000091, 10000000000313, 100000000000261, 1000000000000273, 10000000000000079, 100000000000000049

Offset: 1

Author

Lekraj Beedassy, Jan 28 2007

Keywords

• nonn
• base

Comments

Smallest n-digit emirp (A006567).

Largest n-digit emirp is given by A114019.

Least emirp (A006567) greater than 10^(n-1). [Jonathan Vos Post, Nov 15 2009]

Palindromes not permitted (with the exception of the first term), so for example 101 is not a term. - Harvey P. Dale, Mar 11 2017

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..100

Crossrefs

Cf. A006567, A031991, A114019, A114018, A127747.

Cf. A000040, A004086, A007500. [Jonathan Vos Post, Nov 15 2009]

Programs

Mathematica

f[n_] := Block[{k = 10^(n - 1), id, rid}, While[ id = IntegerDigits[k]; rid = Reverse[id]; ! PrimeQ[k] || ! PrimeQ[FromDigits[rid]] || id == rid, k++ ]; k]; Table[f[n], {n, 2, 19}] (* Ray Chandler, Jan 30 2007 *)
sndp[n_]:=Module[{np=NextPrime[10^(n+1)]},While[PalindromeQ[np] || !PrimeQ[ IntegerReverse[ np]],np= NextPrime[np]];np]; Join[{2},Array[sndp,20,0]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Mar 11 2017 *)

Extensions

Edited and extended by Ray Chandler, Jan 30 2007