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A096774
Numbers k such that 9*10^k + 7 is prime.
2
1, 2, 3, 4, 5, 15, 19, 20, 46, 52, 53, 192, 380, 588, 776, 906, 1350, 1736, 2914, 7508, 15710, 16453, 17488, 18109, 21604, 25891, 26725, 34838, 67468
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
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
Cf. A100998.
Sequence in context: A202423 A171593 A227535 * A201356 A183528 A145029
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