OFFSET
1,2
COMMENTS
a(19) > 2*10^5. - Robert Price, May 24 2015
LINKS
Makoto Kamada, Prime numbers of the form 400...009.
Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers.
FORMULA
a(n) = A101715(n-1) + 1.
EXAMPLE
n = 2, 4, 5, 8, 9 are members since 409, 40009, 400009, 400000009 and 4000000009 are all prime.
MATHEMATICA
Do[ If[ PrimeQ[4*10^n + 9], Print[n]], {n, 0, 10000}]
PROG
(PARI) is(n)=ispseudoprime(4*10^n+9) \\ Charles R Greathouse IV, Jun 12 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Julien Peter Benney (jpbenney(AT)ftml.net), Jan 15 2005
EXTENSIONS
a(10)=2038 from Joao da Silva (zxawyh66(AT)yahoo.com), Sep 30 2005
a(11)-a(12) from Kamada data by Robert Price, Dec 13 2010
Edited by Ray Chandler, Dec 23 2010
a(13)-a(18) from Robert Price, May 24 2015
STATUS
approved