A103967 Numbers n such that the string n1n is the decimal expansion of a prime number.

3, 9, 17, 21, 27, 29, 39, 41, 47, 51, 59, 71, 81, 87, 89, 113, 117, 119, 131, 137, 141, 159, 161, 177, 189, 201, 239, 263, 287, 291, 299, 333, 359, 371, 377, 389, 393, 399, 443, 459, 461, 467, 471, 489, 509, 539, 573, 603, 623, 653, 657, 659, 663, 671, 681

Offset

1,1

Comments

All terms are odd and not multiples of 5. - Zak Seidov, Oct 29 2014

Links

Zak Seidov, Table of n, a(n) for n = 1..10000

Example

n=3 is in the sequence because n1n = 313 is prime.
n=41 is in the sequence because n1n = 41141 is prime.
n=89 is in the sequence because n1n = 89189 is prime.

Mathematica

Reap[Do[If[Mod[n, 5]>0&&PrimeQ[ToExpression[ToString[n]<>"1"<>ToString[n]]], Sow[n]], {n, 3, 1000, 2}]][[2, 1]] (* Zak Seidov, Oct 29 2014 *)

Prog

(Magma) [ n: n in [0..800] | IsPrime(Seqint(Intseq(n) cat [1] cat Intseq(n))) ]; // Klaus Brockhaus, Feb 03 2011

Crossrefs

Cf. A249374.

Sequence in context: A106676 A050795 A050797 * A032400 A329422 A004621

Adjacent sequences: A103964 A103965 A103966 * A103968 A103969 A103970

Keyword

base,nonn

Author

Parthasarathy Nambi, Mar 30 2005

Status

approved