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%I #7 Mar 14 2015 16:58:38
%S 15,18,19,34,36,39,48,52,57,60,67,75,79,81,85,96,97,1005,1020,1030,
%T 1047,1054,1062,1065,1074,1084,1086,1090,1096,1108,1128,1152,1153,
%U 1164,1171,1173,1179,1182,1185,1189,1213,1215,1219,1228,1231,1233,1257,1269,1279
%N Values of n for which the concatenation 7nn7 (from sequence A100897) are primes.
%e The number 715157 is prime and corresponds to n=15.
%e The number 7100510057 is prime and corresponds to n=1005.
%t fQ[n_] := Block[{id = IntegerDigits[n]}, PrimeQ[ FromDigits[ Join[{7}, id, id, {7}]]]]; Select[ Range[1290], fQ[ # ] &] (* _Robert G. Wilson v_, Jan 14 2004 *)
%Y The full sequence of integers of the form 7nn7 is A100897. The primes that correspond to these values of n are sequence A102501.
%K easy,nonn,base
%O 1,1
%A Mark Hudson (mrmarkhudson(AT)hotmail.com), Jan 13 2005
%E More terms from _Robert G. Wilson v_, Jan 14 2005
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