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%I #8 Nov 21 2013 12:49:29
%S 101761,113569,127449,131769,137641,149769,167281,199809,349281,
%T 439569,463761,491401,641601,683929,797449
%N Six-digit squares that are concatenation of two 3-digit primes.
%C a(n)=(A153048(n))^2.
%C There are exactly 15 such numbers.
%t c = 0; t = 1000; re = Sort[Reap[Do[If[PrimeQ[p], Do[If[PrimeQ[q], r = p*t + q; s = Sqrt[r]; If[s == Floor[s], c++; Sow[r]]], {q, 101, 999, 2}]], {p, 101, 999, 2}]][[2, 1]]]
%t concatpQ[n_]:=Module[{idn=IntegerDigits[n],a,b},a=FromDigits[Take[idn,3]];b=FromDigits[Take[idn,-3]];IntegerLength[a]==IntegerLength[b]==3 && PrimeQ[a]&&PrimeQ[b]]; Select[Range[316,1000]^2,concatpQ] (* _Harvey P. Dale_, Mar 09 2012 *)
%Y Cf. A153048.
%K fini,full,nonn,base
%O 1,1
%A _Zak Seidov_, Dec 17 2008
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