OFFSET
1,2
COMMENTS
a(38) > 3*10^5. - Robert Price, Jul 10 2023
LINKS
Makoto Kamada, Prime numbers of the form 700...009.
Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers.
FORMULA
a(n) = A101130(n) + 1.
EXAMPLE
k=2 we get 7*10^2+9 = 7*100+9 = 709, which is prime.
MATHEMATICA
Do[ If[ PrimeQ[ 7*10^n + 9], Print[ n ]], {n, 0, 10000}] (* Robert G. Wilson v, Jan 19 2005 *)
Select[Range[0, 10000], PrimeQ[7 10^# + 9] &] (* Vincenzo Librandi, Sep 06 2015 *)
PROG
(Magma) [n: n in [0..400] |IsPrime(7*10^n + 9)]; // Vincenzo Librandi, Sep 06 2015
(PARI) is(n)=ispseudoprime(7*10^n+9) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
more,nonn
AUTHOR
Julien Peter Benney (jpbenney(AT)ftml.net), Sep 05 2004
EXTENSIONS
a(19)-a(27) from Robert G. Wilson v, Jan 19 2005
a(28)-a(31) from Kamada data by Robert Price, Dec 14 2010
a(32)-a(35) from Robert Price, Sep 05 2015
a(36)-a(37) from Robert Price, Jul 10 2023
STATUS
approved