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%I #9 May 08 2016 08:51:01
%S 53,347,431,641,647,821,1709,1973,2081,2591,2657,2963,4073,4139,4643,
%T 4787,5039,5483,5657,6029,6791,6917,6959,7127,7673,8273,8693,8807,
%U 8849,9221,9311,9689,10139,10457,11423,12503,12743,13619,13913,14549
%N Primes p such that the concatenations p//1331 and 1331//p are both prime numbers (for naturals see A174355).
%C See comments and references for A173836, A174213.
%H Harvey P. Dale, <a href="/A174441/b174441.txt">Table of n, a(n) for n = 1..1000</a>
%e 531331 = prime(43928), 133153 = prime(12427) => p(1) = 53 = prime(16).
%e 3471331 = prime(248286), 1331347 = prime(102237) => p(2) = 347 = prime(69).
%e 139131331 = prime(7865788), 133113913 = prime(7544750) => p(39) = 13913 = prime(1645).
%t Select[Prime[Range[2000]],AllTrue[{#*10^4+1331,1331*10^IntegerLength[ #]+#}, PrimeQ]&] (* The program uses the AllTrue function from Mathematica version 10 *) (* _Harvey P. Dale_, May 08 2016 *)
%o (PARI) isok(n) = isprime(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, A174355.
%K base,nonn
%O 1,1
%A Eva-Maria Zschorn (e-m.zschorn(AT)zaschendorf.km3.de), Mar 20 2010
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