A238499 Primes which are the concatenation of two primes in exactly three ways.

3137, 3797, 13997, 19937, 19997, 23911, 23929, 29173, 29311, 31193, 37337, 37397, 43397, 59929, 73331, 78737, 79337, 103997, 109397, 127997, 139967, 173347, 173359, 193337, 193373, 193877, 199337, 199373, 199967, 229373, 233113, 233329, 233353, 233617

Offset

1,1

Links

Giovanni Resta, Table of n, a(n) for n = 1..10000

Example

13997 is in the sequence because 13, 997, 139, 97, 1399 and 7 are all primes, so there are three ways.

Mathematica

spl[n_] := Block[{d = IntegerDigits@n, c = 0, z}, z = Length@d; Do[If[PrimeQ@ FromDigits@ Take[d, k] && d[[k + 1]] > 0 && PrimeQ@ FromDigits@ Take[d, k - z], c++], {k, z - 1}]; c]; Select[ Prime@ Range@ 20000, spl[#] == 3 &] (* Giovanni Resta, Mar 03 2014 *)

Crossrefs

Cf. A105184, A238056, A238057, A238500.

Sequence in context: A284984 A061048 A250849 * A176790 A086103 A267721

Adjacent sequences: A238496 A238497 A238498 * A238500 A238501 A238502

Keyword

nonn,base

Author

Colin Barker, Feb 27 2014

Status

approved