A036976 - OEIS

%I #7 Jul 29 2012 11:36:19

%S 1,3,7,9,17,23,27,39,51,63,69,81,93,119,121,127,137,161,193,199,203,

%T 209,233,271,301,311,313,323,331,337,343,359,361,367,371,373,431,439,

%U 443,451,463,469,479,481,497,503,523,557,577,583,587,607,641,661,677

%N Becomes a prime if a 1 is inserted before each digit.

%e E.g. 27 -> 1217 is prime.

%t Select[Range[700],PrimeQ[FromDigits[Join[{1},Riffle[ IntegerDigits[ #],1]]]]&] (* _Harvey P. Dale_, Jul 24 2012 *)

%Y Cf. A036977.

%K nonn,base,easy

%O 0,2

%A _N. J. A. Sloane_.

%E More terms from _Erich Friedman_.