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A103056 Numbers n such that 7*10^n + 3*R_n + 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
0, 1, 2, 5, 7, 85, 345, 1595, 2105, 6386, 9119, 9332, 14707, 72560 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Also numbers n such that (22*10^n+17)/3 is prime.

a(15) > 10^5. - Robert Price, Sep 26 2015

LINKS

Table of n, a(n) for n=1..14.

Makoto Kamada, Prime numbers of the form 733...339.

Index entries for primes involving repunits.

FORMULA

a(n) = A101138(n-1) + 1 for n>1.

EXAMPLE

For n=0, (22*10^n+17)/3 = 13 which is a prime so 0 is a term.

MATHEMATICA

Do[ If[ PrimeQ[(22*10^n + 17)/3], Print[n]], {n, 0, 10000}]

CROSSREFS

Cf. A002275, A101138.

Sequence in context: A293592 A042257 A343833 * A041445 A265815 A041961

Adjacent sequences:  A103053 A103054 A103055 * A103057 A103058 A103059

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Jan 19 2005

EXTENSIONS

a(13) from Kamada data by Robert Price, Dec 14 2010

Inserted a(1) = 0 by Robert Price, Sep 26 2015

a(14) from Robert Price, Sep 26 2015

STATUS

approved

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Last modified September 27 04:10 EDT 2021. Contains 347673 sequences. (Running on oeis4.)