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A056716 Numbers n such that 6*10^n-1 is prime. 4
0, 1, 2, 4, 5, 7, 10, 13, 22, 23, 28, 34, 40, 61, 73, 361, 490, 613, 1624, 2000, 2994, 4301, 4332, 18668, 32544, 34936, 267598, 270658, 293134, 319889, 414508 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Also numbers n such that 5*10^n + 9*R_n is prime, where R_n = 11...1 is the repunit (A002275) of length n.

Next term is > 15000. - Hugo Pfoertner, Feb 12 2004

LINKS

Table of n, a(n) for n=1..31.

Makoto Kamada, Prime numbers of the form 599...99.

Index entries for primes involving repunits

MATHEMATICA

Do[ If[ PrimeQ[ 6*10^n - 1], Print[n]], {n, 0, 5000}]

PROG

(PARI) is(n)=ispseudoprime(6*10^n-1) \\ Charles R Greathouse IV, Feb 20 2017

CROSSREFS

Cf. A056805 (6*10^n+1 is prime).

Sequence in context: A226807 A211523 A062463 * A223729 A190235 A023181

Adjacent sequences:  A056713 A056714 A056715 * A056717 A056718 A056719

KEYWORD

hard,nonn,more

AUTHOR

Robert G. Wilson v, Aug 11 2000

EXTENSIONS

More terms from Hugo Pfoertner, Feb 12 2004

3 more terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Dec 30 2007

a(27)-a(31) from Kamada data by Robert Price, Oct 19 2014

STATUS

approved

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Last modified April 19 03:11 EDT 2019. Contains 322237 sequences. (Running on oeis4.)