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A088275
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Numbers n such that 10^n + 9 is prime.
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23
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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; internal format)
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OFFSET
| 1,2
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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. [From Robert Price (pamandbobprice(AT)yahoo.com), Aug 14 2010]
No other terms <=100,000. - [From Robert Price (pamandbobprice(AT)yahoo.com), March 3 2011]
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LINKS
| Makoto Kamada, Factorizations of 100...009.
Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers.
Index entries for primes involving repunits.
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EXAMPLE
| 4 is a member since 10^4 + 9 = 10009 is a prime.
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MATHEMATICA
| Do[ If[ PrimeQ[ 10^n + 9], Print[n]], {n, 0, 10000}] (from Robert G. Wilson v Dec 16 2004)
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CROSSREFS
| Cf. A049054, A088274.
Sequence in context: A119721 A098969 A145027 * A014281 A086865 A192988
Adjacent sequences: A088272 A088273 A088274 * A088276 A088277 A088278
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KEYWORD
| nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Sep 28 2003
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EXTENSIONS
| a(8)-a(16) from Ray Chandler (rayjchandler(AT)sbcglobal.net), 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 (zevi_35711(AT)yahoo.com), Dec 22 2007
a(21)=92691 from Robert Price (pamandbobprice(AT)yahoo.com), Mar 03 2011
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