OFFSET
1,2
COMMENTS
Also numbers n such that 5*10^n + 9*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
a(23) > 2*10^5. - Robert Price, Aug 07 2015
LINKS
FORMULA
a(n) = A101590(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[6*10^n - 7], Print[n]], {n, 0, 10000}]
PROG
(PARI) is(n)=ispseudoprime(6*10^n-7) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 18 2005
EXTENSIONS
Addition of a(20)-a(22) from Kamada data by Robert Price, Dec 09 2010
STATUS
approved