A032703 - OEIS

%I #15 Aug 13 2024 11:48:33

%S 1,3,12,18,19,22,25,27,30,33,36,37,39,46,49,51,54,57,58,63,67,69,70,

%T 76,82,85,88,91,93,105,108,109,112,115,118,123,127,132,139,148,151,

%U 153,154,160,172,174,175,177,189,198,199,205,214,219,225,226,232,234

%N Numbers k such that k prefixed by '3' and followed by '1' is prime.

%H Robert Israel, <a href="/A032703/b032703.txt">Table of n, a(n) for n = 1..10000</a>

%p seq(op(select(x -> isprime(3*10^d+10*x+1),[$10^(d-2)..10^(d-1)-1])),d=2..4); # _Robert Israel_, Oct 22 2018

%t Select[Range[250],PrimeQ[FromDigits[Join[{3}, IntegerDigits[#], {1}]]]&]  (* _Harvey P. Dale_, Mar 28 2011 *)

%Y Cf. A032702-A032733.

%K nonn,base

%O 1,2

%A _Patrick De Geest_, May 15 1998

%E Offset changed to 1 by _Robert Israel_, Oct 22 2018