OFFSET

1,2

COMMENTS

Also numbers n such that 4*10^n + 9*R_n - 8 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

a(22) > 2*10^5. - Robert Price, May 30 2015

LINKS

FORMULA

a(n) = A101738(n) + 1.

MATHEMATICA

Do[ If[ PrimeQ[5*10^n - 9], Print[n]], {n, 0, 10000}]

PROG

(PARI) is(n)=ispseudoprime(5*10^n-9) \\ Charles R Greathouse IV, Jun 06 2017

CROSSREFS

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Jan 17 2005

EXTENSIONS

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

Addition of a(17)-a(19) from Kamada data by Robert Price, Dec 10 2010

a(20)-a(21) from Robert Price, May 30 2015

STATUS

approved