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!)
A111391 Numbers n such that 11*10^n - 1 is prime. 1
1, 9, 11, 17, 22, 29, 36, 37, 52, 166, 448, 2011, 3489, 4871, 6982, 10024, 16974, 33287, 47364, 58873, 126160 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that 10^(n+1) + (10^n-1) is a prime.

LINKS

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

Gary Barnes, Primes of the form k*10^n-1

MATHEMATICA

Do[ If[ PrimeQ[10^(n + 1) + (10^n - 1)], Print[n]], {n, 9500}]

CROSSREFS

Cf. A096209.

Sequence in context: A075824 A228951 A108113 * A077788 A137018 A182391

Adjacent sequences:  A111388 A111389 A111390 * A111392 A111393 A111394

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Nov 15 2005

EXTENSIONS

a(16)-a(19) from Ray Chandler, Sep 16 2013

a(20)-a(21) from P. Kurtovic submitted by Ray Chandler, Sep 17 2013

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 5 15:57 EST 2016. Contains 278770 sequences.