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A096774 Numbers n such that 9*10^n + 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 (list; graph; refs; listen; history; text; internal format)
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 (zevi_35711(AT)yahoo.com), Aug 18 2004

a(30) > 2*10^5. - Robert Price, Oct 16 2015

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

n = 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 (zevi_35711(AT)yahoo.com), 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

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Last modified December 7 17:09 EST 2016. Contains 278888 sequences.