

A095714


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


15



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 n such that 10^n  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: A002396 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 (zevi_35711(AT)yahoo.com), 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



