OFFSET
1,2
COMMENTS
Also numbers n such that 6*10^n + 9*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
a(26) > 2*10^5. - Robert Price, Aug 17 2015
LINKS
FORMULA
a(n) = A101542(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[7*10^n - 3], Print[n]], {n, 0, 10000}]
PROG
(PARI) is(n)=ispseudoprime(7*10^n-3) \\ Charles R Greathouse IV, Jun 12 2017
CROSSREFS
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 18 2005
EXTENSIONS
a(19)-a(24) from Kamada data by Robert Price, Dec 14 2010
a(25) from Robert Price, Aug 17 2015
STATUS
approved