OFFSET
1,2
COMMENTS
No others less than 9000. - Julien Peter Benney (jpbenney(AT)ftml.net), Jan 15 2005
No others less than 39254. - Dirk Augustin, Oct 24 2006
2730, 2841 and 4562 all give primes. - Joao da Silva (zxawyh66(AT)yahoo.com), Sep 30 2005
Verified existing terms. No other terms less than 40001. - Robert Price, Aug 14 2010
No other terms <= 100000. - Robert Price, Mar 03 2011
a(23) > 3*10^5. - Robert Price, Oct 26 2023
LINKS
Makoto Kamada, Prime numbers of the form 100...009.
Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers.
FORMULA
a(n) = A102008(n) + 1.
EXAMPLE
4 is a member since 10^4 + 9 = 10009 is a prime.
MATHEMATICA
Do[ If[ PrimeQ[ 10^n + 9], Print[n]], {n, 0, 10000}] (* Robert G. Wilson v, Dec 16 2004 *)
PROG
(PARI) is(n)=isprime(10^n + 9) \\ Charles R Greathouse IV, Apr 29 2015
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Amarnath Murthy, Sep 28 2003
EXTENSIONS
a(8)-a(16) from Ray Chandler, Oct 10 2003
a(17) from Julien Peter Benney (jpbenney(AT)ftml.net), Jan 15 2005
a(18) (a PRP) found by Dirk Augustin, Oct 16 2006
a(19)-a(20) (probable primes), found with WinPFGW. No others less than 60400. - Jason Earls, Dec 22 2007
a(21) from Robert Price, Mar 03 2011
a(22) from Robert Price, Oct 26 2023
STATUS
approved