A105435 Primes which with a 1 prepended remain prime.

3, 7, 13, 31, 37, 67, 73, 79, 97, 103, 109, 151, 163, 181, 193, 223, 229, 277, 283, 307, 367, 373, 409, 433, 439, 487, 499, 523, 571, 601, 607, 613, 619, 709, 733, 787, 811, 823, 877, 907, 997, 1069, 1087, 1093, 1117, 1171, 1213, 1279, 1321, 1399, 1423, 1447

Offset: 1

Author

Lekraj Beedassy, Apr 08 2005

Keywords

• nonn
• base

Links

• T. D. Noe, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A023237.

Programs

Maple

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 Sellers, Apr 09 2005

Mathematica

Select[ Prime[ Range[ 230]], PrimeQ[ FromDigits[ Join[{1}, IntegerDigits[ # ]]]] &] (* Robert G. Wilson v, Apr 09 2005 *)
Select[Prime[Range[250]],PrimeQ[10^IntegerLength[#]+#]&] (* Harvey P. Dale, May 30 2023 *)

Extensions

Corrected and extended by Robert G. Wilson v and James Sellers, Apr 09 2005