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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, Aug 18 2004 a(30) > 2*10^5. - Robert Price, Oct 16 2015 LINKS Makoto Kamada, Prime numbers of the form 900...007. Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers. 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, 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 January 24 00:05 EST 2022. Contains 350515 sequences. (Running on oeis4.)