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%I #6 Feb 01 2016 12:23:28
%S 1,19,41,43,47,61,67,71,73,83,107,149,211,217,221,269,277,319,437,443,
%T 523,547,553,607,619,647,679,697,817,863,877,899,1171,1283,1297,1379,
%U 1481,1547,1621,1853,1867,1967,1993,1997,2021,2053,2107,2357,2359,2393
%N Numbers n such that the strings n9n and 9n9 are both prime.
%H Harvey P. Dale, <a href="/A090265/b090265.txt">Table of n, a(n) for n = 1..1000</a>
%e 41 is a member as 41941 and 9419 are both prime.
%t n9Q[n_]:=Module[{idn=IntegerDigits[n]},AllTrue[{FromDigits[Join[idn,{9}, idn]],FromDigits[ Join[{9},idn,{9}]]},PrimeQ]]; Select[Range[2500],n9Q] (* The program uses the AllTrue function from Mathematica version 10 *) (* _Harvey P. Dale_, Feb 01 2016 *)
%Y Cf. A090262, A090263, A090264.
%K base,nonn
%O 1,2
%A _Amarnath Murthy_, Nov 28 2003
%E More terms from mohammed bouayoun (bouyao(AT)wanadoo.fr), Feb 02 2004
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