OFFSET
1,2
COMMENTS
k must be even since 12*10^k + 1 is divisible by 11 if k is odd. - Robert G. Wilson v, Feb 12 2018
a(7) > 27440. - Robert G. Wilson v, Feb 17 2018
a(8) > 10^5. - Jeppe Stig Nielsen, Jan 31 2023
EXAMPLE
13 and 1201 are prime, so 0 and 2 are the initial values.
MATHEMATICA
ParallelMap[ If[ PrimeQ[12*10^# +1], #, Nothing] &, 2 + 6Range@ 4500] (* Robert G. Wilson v, Feb 13 2018 *)
PROG
(PARI) isok(k) = isprime(12*10^k + 1); \\ Altug Alkan, Mar 04 2018
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Patrick A. Thomas, Feb 12 2018
EXTENSIONS
a(5) from Robert G. Wilson v, Feb 12 2018
a(6) from Robert G. Wilson v, Feb 13 2018
a(7) from Jeppe Stig Nielsen, Jan 28 2023
STATUS
approved