login
This site is supported by donations to The OEIS Foundation.

 

Logo

Annual Appeal: Please make a donation (tax deductible in USA) to keep the OEIS running. Over 5000 articles have referenced us, often saying "we discovered this result with the help of the OEIS".

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A103092 Numbers n such that 9*10^n-7 is prime. 1
0, 1, 6, 9, 10, 12, 13, 23, 61, 194, 233, 549, 765, 973, 1061, 1186, 1853, 3713, 6789, 7254, 7765, 9025, 10855, 23640, 31440, 31839, 32287, 120342, 132148 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Also numbers n such that 8*10^n + 9*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

a(30) > 2*10^5. - Robert Price, Sep 04 2015

LINKS

Table of n, a(n) for n=1..29.

Makoto Kamada, Prime numbers of the form 899...993.

Index entries for primes involving repunits.

FORMULA

a(n) = A101079(n-1) + 1 for n>1.

EXAMPLE

For n=0, 9*10^n-7=2 which is prime, so 0 is in the sequence.

MATHEMATICA

Do[ If[ PrimeQ[9*10^n - 7], Print[n]], {n, 0, 10000}]

PROG

(MAGMA) [n: n in [0..300] | IsPrime(9*10^n-7)]; // Vincenzo Librandi, Sep 05 2015

CROSSREFS

Cf. A002275, A101079.

Sequence in context: A124257 A066385 A226913 * A104523 A091886 A111774

Adjacent sequences:  A103089 A103090 A103091 * A103093 A103094 A103095

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Jan 19 2005

EXTENSIONS

One more term from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

a(23)-a(26) from Kamada data by Robert Price, Dec 14 2010

Inserted a(1)=0 by Robert Price, Sep 04 2015

a(28)-a(29) from Robert Price, Sep 04 2015

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified December 2 17:24 EST 2016. Contains 278682 sequences.