

A056662


Numbers n such that 90*R_n + 7 is prime, where R_n = 11...1 is the repunit (A002275) of length n.


3



0, 1, 2, 16, 139, 989, 1886, 3529, 5995, 13819, 21872, 26044, 87719, 232598
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OFFSET

1,3


COMMENTS

Also numbers n such that 10^(n+1)  3 is a prime number.


LINKS

Table of n, a(n) for n=1..14.
Makoto Kamada, Prime numbers of the form 99...997.
Index entries for primes involving repunits


FORMULA

a(n) = A089675(n)  1.  Robert Price, Nov 01 2014


MATHEMATICA

Do[ If[ PrimeQ[ 90*(10^n  1)/9 + 7 ], Print[n]], {n, 0, 1250}]


CROSSREFS

Cf. A002275, A089675.
Sequence in context: A001252 A067058 A002302 * A151402 A199565 A003768
Adjacent sequences: A056659 A056660 A056661 * A056663 A056664 A056665


KEYWORD

hard,nonn


AUTHOR

Robert G. Wilson v, Aug 09 2000


EXTENSIONS

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(13)a(14) derived from A089675 by Robert Price, Nov 01 2014


STATUS

approved



