

A095714


Numbers k such that 9*R_k  8 is prime, where R_k = 11...1 is the repunit (A002275) of length k.


16



3, 5, 7, 33, 45, 105, 197, 199, 281, 301, 317, 1107, 1657, 3395, 35925, 37597, 64305, 80139, 221631
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OFFSET

1,1


COMMENTS

Also numbers k such that 10^k  9 is a prime.


LINKS

Table of n, a(n) for n=1..19.
Makoto Kamada, Prime numbers of the form 99...991.
Index entries for primes involving repunits


FORMULA

a(n) = A056696(n) + 1.


EXAMPLE

a(2) = 5, since 10^5  9 = 99991, which is prime.


MATHEMATICA

Do[ If[ PrimeQ[10^n  9], Print[n]], {n, 0, 7000}]


CROSSREFS

Cf. A002275, A093177, A056696.
Sequence in context: A302099 A029508 A256935 * A137864 A256154 A069969
Adjacent sequences: A095711 A095712 A095713 * A095715 A095716 A095717


KEYWORD

nonn


AUTHOR

Alonso del Arte, Jul 07 2004


EXTENSIONS

a(12)  a(14) from Robert G. Wilson v, Oct 15 2004
a(15)  a(16) from Jason Earls, Jan 07 2008
a(17)  a(19) from Alexander Gramolin, May 13 2011
Edited by Ray Chandler, Feb 26 2012
Title corrected by Robert Price, Sep 06 2014


STATUS

approved



