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A238500 Primes which are the concatenation of two primes in exactly four ways. 2
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified January 23 11:42 EST 2022. Contains 350512 sequences. (Running on oeis4.)