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A056663 Numbers k such that 80*R_k + 9 is prime, where R_k = 11...1 is the repunit (A002275) of length k. 2
1, 13, 16, 34, 4174, 4471, 9811, 12259, 12340, 13759, 14575, 53410, 144682, 148327 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also numbers k such that (8*10^(k+1) + 1)/9 is prime.

a(15) > 2*10^5. - Robert Price, Nov 01 2014

LINKS

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

Makoto Kamada, Prime numbers of the form 88...889.

Index entries for primes involving repunits

FORMULA

a(n) = A096508(n) - 1. - Robert Price, Nov 01 2014

MATHEMATICA

Do[ If[ PrimeQ[ 80*(10^n - 1)/9 + 9 ], Print[n]], {n, 0, 30000}]

CROSSREFS

Cf. A002275, A096508.

Sequence in context: A280062 A132947 A205876 * A274978 A103230 A217179

Adjacent sequences:  A056660 A056661 A056662 * A056664 A056665 A056666

KEYWORD

hard,nonn

AUTHOR

Robert G. Wilson v, Aug 09 2000

EXTENSIONS

Intermediate missing terms 9811 (from M. Kamada), 12259, 12340, 13759 added by Serge Batalov, Dec 14 2008

a(12)-a(14) derived from A096508 by Robert Price, Nov 01 2014

STATUS

approved

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Last modified June 20 04:43 EDT 2021. Contains 345157 sequences. (Running on oeis4.)