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A103019 Numbers n such that 5*10^n + 7*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
2, 6, 9, 27, 30, 48, 141, 150, 372, 422, 1097, 3570, 4607, 5289, 10734, 11550, 32604, 42470, 46311 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also numbers n such that (52*10^n-61)/9 is prime.

LINKS

Table of n, a(n) for n=1..19.

Makoto Kamada, Factorizations of 577...771.

Index entries for primes involving repunits.

MATHEMATICA

Do[ If[ PrimeQ[(52*10^n - 61)/9], Print[n]], {n, 0, 10000}]

CROSSREFS

Sequence in context: A243558 A244427 A121624 * A101823 A242421 A093397

Adjacent sequences:  A103016 A103017 A103018 * A103020 A103021 A103022

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Jan 18 2005

EXTENSIONS

Addition of a(15)-a(16) from Kamada data by Robert Price, Dec 12 2010

a(17)-a(19) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

STATUS

approved

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Last modified December 20 09:43 EST 2014. Contains 252241 sequences.