OFFSET
1,2
COMMENTS
Also numbers n such that 4*10^n + 9*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
a(20) > 2*10^5. - Robert Price, Sep 15 2015
LINKS
FORMULA
a(n) = A101739(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[5*10^n - 7], Print[n]], {n, 0, 10000}]
PROG
(PARI) is(n)=ispseudoprime(5*10^n-7) \\ Charles R Greathouse IV, Jun 06 2017
CROSSREFS
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 17 2005
EXTENSIONS
Addition of a(17)-a(18) from Kamada data by Robert Price, Dec 10 2010
a(19) from Robert Price, Sep 15 2015
STATUS
approved