A248046 - OEIS

%I #31 Oct 08 2014 16:52:40

%S 5,73,337,409,701,827,5449,5477,5939,6841,7417,8353,8573,9109,9227,

%T 9311,9733,9767,32569,34319,34327,34501,35933,35999,38371,38449,38923,

%U 38953,39023,39367,39671,40531,40973,42701,43543,44651,45259,46021,47623,48311,49531,50923,54133,54437,54547

%N Primes p such that p^2 is the concatenation of two k-digit primes where k is half the length of p^2.

%H Jens Kruse Andersen, <a href="/A248046/b248046.txt">Table of n, a(n) for n = 1..10000</a>

%e 73 is prime, and 73^2 = 5329 is the concatenation of two 2-digit primes (53 and 29). So 73 is a member of this sequence.

%e 929 is not in the sequence since 929^2 = 863041, where 863 is a 3-digit prime but 041 is a 2-digit prime. - _Jens Kruse Andersen_, Oct 06 2014

%o (PARI)

%o forprime(p=1,10^5,d=digits(p^2);if((#d)%2==0,if(isprime((p^2)\(10^(#d/2)))&&isprime((p^2)%(10^(#d/2)))&&#Str((p^2)%(10^(#d/2)))==#d/2,print1(p,", "))))

%Y Cf. A105184, A030461, A153048, A153164, A080906, A248208.

%K nonn,base

%O 1,1

%A _Derek Orr_, Oct 03 2014

%E Terms and program corrected by _Derek Orr_ to match definition, thanks to _Jens Kruse Andersen_