A238500 Primes which are the concatenation of two primes in exactly four ways.

233347, 233911, 239929, 337397, 373613, 379397, 733331, 796337, 1321997, 1933331, 2333347, 2333533, 2339929, 2392333, 2393257, 2393761, 2939971, 3136373, 3165713, 3217337, 3319733, 3499277, 3539311, 3727397, 3733967, 3739103, 3739199, 3739397, 3739433

Offset

1,1

Links

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

Example

233347 is in the sequence because 2, 33347, 23, 3347, 233, 347, 2333 and 47 are all primes, so there are four 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@ 250000, spl[#] == 4 &] (* Giovanni Resta, Mar 03 2014 *)

Crossrefs

Cf. A105184, A238056, A238057, A238499.

Sequence in context: A015331 A250697 A250682 * A224656 A250858 A233902

Adjacent sequences: A238497 A238498 A238499 * A238501 A238502 A238503

Keyword

nonn,base

Author

Colin Barker, Feb 27 2014

Status

approved