OFFSET

1,2

COMMENTS

Also numbers n such that (8*10^n-17)/9 is prime.

The numbers corresponding to a(1)-a(15) are certified prime, the numbers corresponding to a(16)-a(20) are probable primes. a(21) > 10^5. - Robert Price, May 20 2014

LINKS

FORMULA

a(n) = A056695(n) + 1. - Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

EXAMPLE

n=6: a(4)=888887 which is prime.

MATHEMATICA

Do[ If[ PrimeQ[ 8(10^n - 1)/9 - 1], Print[n]], {n, 0, 5000}] (* Robert G. Wilson v, Oct 15 2004; corrected by Derek Orr, Sep 06 2014 *)

PROG

(PARI)

for(n=1, 10^4, if(ispseudoprime(8*(10^n-1)/9-1), print1(n, ", "))) \\ Derek Orr, Sep 06 2014

CROSSREFS

KEYWORD

more,nonn

AUTHOR

Labos Elemer, Jul 15 2004

EXTENSIONS

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

a(18)-a(20) discovered and reported to Makoto Kamada by Erik Branger; added to OEIS by Robert Price, May 20 2014

a(21)-a(23) from Kamada data by Tyler Busby, Apr 23 2024

STATUS

approved