

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
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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



