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 A088275 Numbers n such that 10^n + 9 is prime. 24
 1, 2, 3, 4, 9, 18, 22, 45, 49, 56, 69, 146, 202, 272, 2730, 2841, 4562, 31810, 43186, 48109, 92691 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS No others less than 9000. - Julien Peter Benney (jpbenney(AT)ftml.net), Jan 15 2005 No others less than 39254. - Dirk Augustin, Oct 24 2006 2730, 2841 and 4562 all give primes. - Joao da Silva (zxawyh66(AT)yahoo.com), Sep 30 2005 Verified existing terms. No other terms less than 40001. - Robert Price, Aug 14 2010 No other terms <= 100,000. - Robert Price, Mar 03 2011 a(22) > 2*10^5. - Robert Price, Oct 11 2015 LINKS Makoto Kamada, Prime numbers of the form 100...009. Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers. FORMULA a(n) = A102008(n) + 1. EXAMPLE 4 is a member since 10^4 + 9 = 10009 is a prime. MATHEMATICA Do[ If[ PrimeQ[ 10^n + 9], Print[n]], {n, 0, 10000}] (* Robert G. Wilson v, Dec 16 2004 *) PROG (PARI) is(n)=isprime(10^n + 9) \\ Charles R Greathouse IV, Apr 29 2015 CROSSREFS Cf. A049054, A088274, A102008. Sequence in context: A235401 A281882 A145027 * A274836 A014281 A220364 Adjacent sequences:  A088272 A088273 A088274 * A088276 A088277 A088278 KEYWORD nonn AUTHOR Amarnath Murthy, Sep 28 2003 EXTENSIONS a(8)-a(16) from Ray Chandler, Oct 10 2003 a(17) from Julien Peter Benney (jpbenney(AT)ftml.net), Jan 15 2005 a(18) (a PRP) found by Dirk Augustin, Oct 16 2006 Two more terms (probable primes), found with WinPFGW. No others less than 60400. - Jason Earls, Dec 22 2007 a(21)=92691 from Robert Price, Mar 03 2011 STATUS approved

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Last modified October 19 18:28 EDT 2018. Contains 316377 sequences. (Running on oeis4.)