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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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified October 19 11:09 EDT 2019. Contains 328216 sequences. (Running on oeis4.)