A096774 Numbers k such that 9*10^k + 7 is prime.

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

Links

Table of n, a(n) for n=1..29.

Makoto Kamada, Prime numbers of the form 900...007.

Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers.

Index entries for primes involving repunits.

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

Adjacent sequences: A096771 A096772 A096773 * A096775 A096776 A096777

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