OFFSET
1,1
COMMENTS
The order is important. 3 does not qualify, because 133 is not a prime, even though 313 is. - N. J. A. Sloane, Aug 19 2014
LINKS
Jens Kruse Andersen, Table of n, a(n) for n = 1..10000
EXAMPLE
81 is included because 18181 is a prime. 137 is included because 1137137 is a prime.
MATHEMATICA
Select[Range[999], PrimeQ[FromDigits[Join[{1}, IntegerDigits[ #], IntegerDigits[ #]]]]&]
PROG
(Python)
from sympy import isprime
for n in range(1, 10**3):
if isprime(int('1'+str(n)+str(n))):
print(n, end=', ')
# Derek Orr, Aug 17 2014
(PARI) s=[]; for(n=1, 10^3, d=length(Str(n)); if(isprime(10^(2*d)+(10^(2*d)-1)/(10^d-1)*n), s=concat(s, n))); s \\ Jens Kruse Andersen, Aug 18 2014
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
Harvey P. Dale, Aug 17 2014
STATUS
approved