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A056722 Numbers n such that 8*10^n + R_n is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
2, 3, 26, 110, 141, 474, 902, 1746, 2997, 3627, 3788, 51162, 71670, 78576, 104942, 122592, 248145 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also numbers n such that (73*10^n-1)/9 is prime.

The next term is > 10000. - Hugo Pfoertner, Oct 21 2004

a(18) > 250,000. - Robert Price, Jan 21 2015

LINKS

Table of n, a(n) for n=1..17.

Makoto Kamada, Prime numbers of the form 811...11.

Index entries for primes involving repunits

MATHEMATICA

Do[ If[ PrimeQ[ 8*10^n + (10^n-1)/9], Print[n]], {n, 0, 5000}]

CROSSREFS

Cf. A002275, A093633.

Sequence in context: A042043 A178196 A258766 * A181225 A143876 A184506

Adjacent sequences:  A056719 A056720 A056721 * A056723 A056724 A056725

KEYWORD

hard,nonn

AUTHOR

Robert G. Wilson v, Aug 11 2000

EXTENSIONS

a(12)-a(17) from Kamada data by Robert Price, Jan 21 2015

STATUS

approved

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Last modified April 22 14:18 EDT 2019. Contains 322349 sequences. (Running on oeis4.)