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%I #9 Jun 05 2024 11:51:13
%S 715157,718187,719197,734347,736367,739397,748487,752527,757577,
%T 760607,767677,775757,779797,781817,785857,796967,797977,7100510057,
%U 7102010207,7103010307,7104710477,7105410547,7106210627,7106510657,7107410747
%N Primes of the concatenated form 7nn7.
%H Harvey P. Dale, <a href="/A102501/b102501.txt">Table of n, a(n) for n = 1..1000</a>
%e 715157 is prime and of the form 7nn7 for n=15.
%e 7100510057 is prime and of the form 7nn7 for n=1005.
%t Select[Table[FromDigits[Join[{7},IntegerDigits[n],IntegerDigits[n],{7}]],{n,1100}],PrimeQ] (* _Harvey P. Dale_, Jun 05 2024 *)
%Y Cf. A102897 for sequence of all numbers of form 7nn7. A102500 for the n values corresponding to the primes in this sequence.
%K easy,nonn,base
%O 1,1
%A Mark Hudson (mrmarkhudson(AT)hotmail.com), Jan 13 2005