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Numbers k such that k prefixed by '1' and followed by '9' is a prime.
1

%I #11 Jul 28 2021 04:25:56

%S 0,3,4,7,9,10,12,22,24,25,27,28,31,39,40,42,43,45,48,49,54,55,57,60,

%T 61,66,69,70,75,78,87,88,94,97,99,105,106,111,114,115,123,127,129,132,

%U 136,139,148,151,154,157,168,169,171,177,178,183,190,193,195,196,204

%N Numbers k such that k prefixed by '1' and followed by '9' is a prime.

%t Select[Range[0,200],PrimeQ@FromDigits[Join[{1},IntegerDigits@#,{9}]]&] (* _Giorgos Kalogeropoulos_, Jul 28 2021 *)

%K nonn,base

%O 1,2

%A _Patrick De Geest_, May 15 1998