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A103031 Numbers n such that 6*10^n + 2*R_n + 7 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
0, 3, 15, 339 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also numbers n such that (56*10^n+61)/9 is prime.

a(5) > 10^5. - Robert Price, Sep 07 2015

LINKS

Table of n, a(n) for n=1..4.

Makoto Kamada, Prime numbers of the form 622...229.

Index entries for primes involving repunits.

FORMULA

a(n) = A101524(n-1) + 1 for n>1.

EXAMPLE

For n=0, (56*10^n+61)/9=13 which is prime, so 0 is in the sequence.

MATHEMATICA

Do[ If[ PrimeQ[(56*10^n + 61)/9], Print[n]], {n, 0, 10000}]

CROSSREFS

Cf. A002275, A101524.

Sequence in context: A036279 A156769 A029758 * A012474 A296940 A193119

Adjacent sequences:  A103028 A103029 A103030 * A103032 A103033 A103034

KEYWORD

bref,more,nonn

AUTHOR

Robert G. Wilson v, Jan 18 2005

EXTENSIONS

Inserted a(1)=0 by Robert Price, Sep 07 2015

STATUS

approved

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Last modified February 22 18:00 EST 2018. Contains 299469 sequences. (Running on oeis4.)