A032711 Numbers k such that the concatenation '2',k,'3' is prime.

2, 3, 6, 8, 9, 11, 14, 15, 20, 21, 24, 27, 29, 33, 38, 39, 42, 47, 50, 54, 59, 63, 66, 68, 69, 71, 75, 80, 83, 84, 90, 95, 96, 101, 102, 114, 116, 119, 128, 131, 132, 138, 143, 149, 150, 152, 156, 161, 167, 168, 171, 177, 180, 186, 189, 194, 200, 201, 206, 207, 209

Offset

1,1

Comments

This sequence is infinite, a consequence of the Prime Number Theorem in arithmetic progressions. - Charles R Greathouse IV, Sep 26 2012

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Example

8 and 21 are in the sequence because 283 and 2213 are primes.

Mathematica

v={}; Do[If[PrimeQ[FromDigits[Join[{2}, IntegerDigits[n], {3}]]], v=Append[v, n]], {n, 260}]; v (* Farideh Firoozbakht, Jun 15 2003 *)
Select[Range[210], PrimeQ[FromDigits[Join[{2}, IntegerDigits[#], {3}]]]&] (* Harvey P. Dale, May 02 2012 *)

Prog

(PARI) for( n=1, 300, isprime(eval(Str(2, n, 3))) & print1(n", ")) \\ M. F. Hasler, Mar 18 2008

Crossrefs

Cf. A083677, A083966, A083969, A092117.

Sequence in context: A013952 A105042 A092114 * A135768 A287659 A047244

Adjacent sequences: A032708 A032709 A032710 * A032712 A032713 A032714

Keyword

nonn,base

Author

Patrick De Geest, May 15 1998

Extensions

Merged with data from duplicate entry A092114. - M. F. Hasler, Mar 18 2008

Status

approved