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Primes with either no internal digits or all internal digits are 9.
18

%I #29 Nov 10 2024 17:20:55

%S 2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,

%T 97,191,193,197,199,293,397,491,499,593,599,691,797,991,997,1993,1997,

%U 1999,2999,4993,4999,6991,6997,7993,8999,19991,19993,19997,49991,49993,49999

%N Primes with either no internal digits or all internal digits are 9.

%H Harvey P. Dale, <a href="/A069684/b069684.txt">Table of n, a(n) for n = 1..252</a> (* All terms with less than 500 digits. *)

%t Join[Prime[Range[25]],Select[Flatten[Table[FromDigits[Join[{d1},PadRight[{},n,9],{d2}]],{n,150},{d1,9},{d2,{1,3,7,9}}]],PrimeQ]] (* _Harvey P. Dale_, Nov 10 2024 *)

%Y Cf. A069675, A069676, A069677, A069678, A069679, A069680, A069681, A069682, A069683.

%K nonn,base

%O 1,1

%A _Amarnath Murthy_, Apr 06 2002

%E Corrected by _Ray Chandler_, Nov 24 2003

%E Offset corrected and name changed by Arkadiusz Wesolowski, Sep 07 2011