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A088275 Numbers n such that 10^n + 9 is prime. 23
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

Table of n, a(n) for n=1..21.

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 (zevi_35711(AT)yahoo.com), Dec 22 2007

a(21)=92691 from Robert Price, Mar 03 2011

STATUS

approved

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Last modified September 26 05:09 EDT 2017. Contains 292502 sequences.