The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A238500 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
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A238500

Primes which are the concatenation of two primes in exactly four ways.
(history; published version)

#6 by Bruno Berselli at Mon Mar 03 08:38:55 EST 2014

STATUS

proposed

approved

#5 by Giovanni Resta at Mon Mar 03 07:06:15 EST 2014

STATUS

editing

proposed

#4 by Giovanni Resta at Mon Mar 03 07:06:08 EST 2014

LINKS

Giovanni Resta, <a href="/A238500/b238500.txt">Table of n, a(n) for n = 1..10000</a>

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 *)

STATUS

proposed

editing

#3 by Colin Barker at Thu Feb 27 14:21:09 EST 2014

STATUS

editing

proposed

#2 by Colin Barker at Thu Feb 27 14:21:04 EST 2014

NAME

allocated for Colin BarkerPrimes which are the concatenation of two primes in exactly four ways.

DATA

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

EXAMPLE

233347 is in the sequence because 2, 33347, 23, 3347, 233, 347, 2333 and 47 are all primes, so there are four ways.

CROSSREFS

Cf. A105184, A238056, A238057, A238499.

KEYWORD

allocated

nonn,base

AUTHOR

Colin Barker, Feb 27 2014

STATUS

approved

editing

#1 by Colin Barker at Thu Feb 27 14:15:36 EST 2014

NAME

allocated for Colin Barker

KEYWORD

allocated

STATUS

approved