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A103015 Numbers n such that 5*10^n + 4*R_n + 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
2, 6, 8, 18, 53, 68, 242, 276, 320, 564, 620, 1782, 2340, 2454, 5765, 15530, 15605, 22938 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also numbers n such that (49*10^n+23)/9 is prime.

a(19) > 10^5. - Robert Price, Jul 29 2015

LINKS

Table of n, a(n) for n=1..18.

Makoto Kamada, Prime numbers of the form 544...447.

Index entries for primes involving repunits.

FORMULA

a(n) = A101580(n) + 1.

MATHEMATICA

Do[ If[ PrimeQ[(49*10^n + 23)/9], Print[n]], {n, 0, 10000}]

CROSSREFS

Cf. A002275, A101580.

Sequence in context: A102656 A163911 A077638 * A098092 A221316 A106164

Adjacent sequences:  A103012 A103013 A103014 * A103016 A103017 A103018

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Jan 18 2005

EXTENSIONS

a(16)-a(18) from Kamada data by Robert Price, Dec 14 2010

STATUS

approved

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Last modified December 7 17:16 EST 2016. Contains 278890 sequences.