A105435 - OEIS

%I #15 May 30 2023 10:51:38

%S 3,7,13,31,37,67,73,79,97,103,109,151,163,181,193,223,229,277,283,307,

%T 367,373,409,433,439,487,499,523,571,601,607,613,619,709,733,787,811,

%U 823,877,907,997,1069,1087,1093,1117,1171,1213,1279,1321,1399,1423,1447

%N Primes which with a 1 prepended remain prime.

%H T. D. Noe, <a href="/A105435/b105435.txt">Table of n, a(n) for n = 1..10000</a>

%p with(numtheory); for i from 1 to 500 do if isprime(10^(ceil(log[10](ithprime(i))))+ithprime(i)) then printf(`%d,`, ithprime(i)) fi: od: # _James A. Sellers_, Apr 09 2005

%t Select[ Prime[ Range[ 230]], PrimeQ[ FromDigits[ Join[{1}, IntegerDigits[ # ]]]] &] (* _Robert G. Wilson v_, Apr 09 2005 *)

%t Select[Prime[Range[250]],PrimeQ[10^IntegerLength[#]+#]&] (* _Harvey P. Dale_, May 30 2023 *)

%Y Cf. A023237.

%K nonn,base

%O 1,1

%A _Lekraj Beedassy_, Apr 08 2005

%E Corrected and extended by _Robert G. Wilson v_ and _James A. Sellers_, Apr 09 2005