%I #9 Aug 21 2015 11:16:53

%S 53,57,153,249,279,329,333,339,347,381,399,431,471,489,641,647,711,

%T 821,851,923,959,987,1169,1239,1313,1383,1479,1547,1563,1589,1611,

%U 1653,1677,1709,1773,1863,1887,1973,2031,2067

%N Natural numbers n such that the concatenations n//1331 and 1331//n are prime numbers.

%C See comments and references for A173836, A174213.

%C Intersection of A173579 and A174213. - _Michel Marcus_, Aug 27 2013

%D Marcus du Sautoy: Die Musik der Primzahlen. Auf den Spuren des groessten Raetsels der Mathematik, Beck, Muenchen 2004

%H Harvey P. Dale, <a href="/A174355/b174355.txt">Table of n, a(n) for n = 1..1000</a>

%e 531331 = prime(43928), 133153 = prime(12427), 53 is smallest term of sequence.

%t Select[Range[2100],AllTrue[{#*10^4+1331,1331*10^IntegerLength[#]+#},PrimeQ]&] (* The program uses the AllTrue function from Mathematica version 10 *) (* _Harvey P. Dale_, Aug 21 2015 *)

%o (PARI) isok(n) = isprime(n*10^4 + 1331) && isprime(1331*10^(length(Str(n))) + n); \\ _Michel Marcus_, Aug 27 2013

%Y Cf. A168327, A168417, A173836, A174213, A174260.

%K base,nonn

%O 1,1

%A Eva-Maria Zschorn (e-m.zschorn(AT)zaschendorf.km3.de), Mar 17 2010