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%I #8 Mar 17 2015 23:12:37
%S 5,7,31,37,41,43,53,59,61,67,73,79,83,101,103,139,151,157,179,197,223,
%T 241,257,263,269,271,283,293,307,311,349,353,389,421,431,461,467,491,
%U 557,593,599,601,607,631,643,647,683,691,701,727,757,769,811,827,839
%N Primes that yield another prime on placing a 3 on both sides (as leading and trailing digits).
%H Harvey P. Dale, <a href="/A069688/b069688.txt">Table of n, a(n) for n = 1..10000</a>
%e 139 is a member as 31393 is also a prime.
%t Select[ Range[1000], PrimeQ[ # ] && PrimeQ[ FromDigits[ Insert[ IntegerDigits[ # ], 3, {{1}, {-1}}]]] &]
%t Select[Prime[Range[200]],PrimeQ[FromDigits[Join[{3},IntegerDigits[#],{3}]]]&] (* _Harvey P. Dale_, Oct 24 2011 *)
%Y Cf. A069687, A069689, A069690.
%K nonn,base
%O 1,1
%A _Amarnath Murthy_, Apr 06 2002
%E Edited and extended by _Robert G. Wilson v_, May 03 2002
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