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A243886 Primes p = prime(n): such that p.n and n.p both are prime, where (.) indicates concatenation.

%I A243886 #10 Jun 15 2014 08:48:55
%S A243886 661,1051,1999,2179,3433,3593,3719,4073,4591,4733,5449,5503,6079,6481,
%T A243886 7109,7211,7489,8293,8513,9901,10273,10529,11821,12721,14107,14591,
%U A243886 14879,15263,15877,18149,19559,22027,22129,22571,23339,24527,25357,26881,27337,34259
%N A243886 Primes p = prime(n): such that p.n and n.p both are prime, where (.) indicates concatenation.
%C A243886 Intersection of A084671 and A166283.
%H A243886 K. D. Bajpai, <a href="/A243886/b243886.txt">Table of n, a(n) for n = 1..10000</a>
%e A243886 661 is in the sequence because 661 = prime(121): Concatenations of [661.121 = 661121] and concatenation of [121.661 = 121661] which are also primes.
%e A243886 1051 is in the sequence because 1051 = prime(177): Concatenation of [1051.177 = 1051177] and concatenation of [177.1051 = 1771051] which are also primes.
%p A243886 with(numtheory): with(StringTools): A243886:= proc() local p,k1,k2; p:=ithprime(n); k1:=parse (cat (p,n)); k2:=parse(cat(n,p)); if isprime(k1)and isprime(k2) then RETURN (p); fi; end: seq(A243886 (), n=1..5000);
%t A243886 Select[Prime [Range[5000]], PrimeQ[FromDigits[Join[IntegerDigits [PrimePi [#]], IntegerDigits [#]]]] && PrimeQ [FromDigits [Join [IntegerDigits[#], IntegerDigits [PrimePi [#]]]]] &]
%Y A243886 Cf. A000040, A084671, A166283.
%K A243886 nonn,base
%O A243886 1,1
%A A243886 _K. D. Bajpai_, Jun 13 2014