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Numbers k such that k concatenated with k+3 is a prime.
3

%I #16 Jul 28 2021 04:19:57

%S 4,8,10,16,44,46,56,58,68,74,86,94,98,100,104,106,136,140,148,154,158,

%T 160,166,176,184,194,206,230,244,250,254,260,266,268,274,286,296,308,

%U 310,328,338,344,346,370,380,388,410,416,430,434,436,440,448,460

%N Numbers k such that k concatenated with k+3 is a prime.

%H Robert Israel, <a href="/A032618/b032618.txt">Table of n, a(n) for n = 1..10000</a>

%p filter:= n -> isprime(n*(10^(1+ilog10(n+3))+1)+3):

%p select(filter, [seq(i,i=4..1000,2)]); # _Robert Israel_, Nov 14 2019

%t Select[Range[500],PrimeQ[FromDigits[Join[IntegerDigits[#], IntegerDigits[ #+3]]]]&] (* _Harvey P. Dale_, Jul 19 2011 *)

%Y Cf. A032608.

%K nonn,base

%O 1,1

%A _Patrick De Geest_, May 15 1998