OFFSET
1,2
COMMENTS
a(1) through a(12) have been certified prime. a(13) through a(19) are all Fermat and Lucas PRPs. No others less than 6300. - Jason Earls, Aug 18 2004
a(30) > 3*10^5. - Robert Price, Jul 10 2023
LINKS
Makoto Kamada, Prime numbers of the form 900...007.
Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers.
FORMULA
a(n) = A100998(n) + 1.
EXAMPLE
k = 5; (9*10^5)+7 = 900007, which is prime.
MATHEMATICA
Do[ If[ PrimeQ[9*10^n + 7], Print[n]], {n, 0, 10000}] (* Robert G. Wilson v, Jan 19 2005 *)
PROG
(PARI) for(n=1, 1e5, if(isprime(9*10^n + 7), print1(n", "))) \\ Altug Alkan, Oct 16 2015
CROSSREFS
KEYWORD
more,nonn
AUTHOR
Julien Peter Benney (jpbenney(AT)ftml.net), Aug 16 2004
EXTENSIONS
More terms from Jason Earls, Aug 18 2004
a(20) from Robert G. Wilson v, Jan 19 2005
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(25)-a(29) from Kamada data by Robert Price, Dec 14 2010
STATUS
approved