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A103023 Numbers n such that 5*10^n + 8*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
2, 6, 8, 20, 108, 288, 306, 462, 20102, 30042 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also numbers n such that (53*10^n-17)/9 is prime.

LINKS

Table of n, a(n) for n=1..10.

Makoto Kamada, Factorizations of 588...887.

Index entries for primes involving repunits.

MATHEMATICA

Do[ If[ PrimeQ[(53*10^n - 17)/9], Print[n]], {n, 0, 10000}]

CROSSREFS

Sequence in context: A134136 A185165 A058775 * A111247 A045656 A129342

Adjacent sequences:  A103020 A103021 A103022 * A103024 A103025 A103026

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Jan 18 2005

EXTENSIONS

Addition of a(9) from Kamada data by Robert Price, Dec 13 2010

a(10) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

STATUS

approved

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Last modified September 1 07:55 EDT 2014. Contains 246289 sequences.