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A056703 Numbers n such that 3*10^n - 1 is prime. 1
0, 1, 3, 6, 7, 19, 27, 43, 55, 207, 1311, 3204, 7050, 9439, 26044, 33058, 34507, 49314, 119292 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Also numbers n such that 2*10^n + 9*R_n is prime, where R_n = 11...1 is the repunit (A002275) of length n.

LINKS

Table of n, a(n) for n=1..19.

Makoto Kamada, Prime numbers of the form 299...99.

Index entries for primes involving repunits

MATHEMATICA

Do[ If[ PrimeQ[ 2*10^n + (10^n-1)], Print[n]], {n, 0, 3000}]

Select[Range[200000], PrimeQ[3*10^#-1]&] (* Harvey P. Dale, Sep 29 2012 *)

PROG

(PARI) is(n)=ispseudoprime(3*10^n-1) \\ Charles R Greathouse IV, Jun 12 2017

CROSSREFS

Sequence in context: A072773 A130049 A259256 * A113534 A103831 A217519

Adjacent sequences:  A056700 A056701 A056702 * A056704 A056705 A056706

KEYWORD

hard,nonn,more

AUTHOR

Robert G. Wilson v, Aug 10 2000

EXTENSIONS

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

STATUS

approved

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Last modified April 19 16:40 EDT 2019. Contains 322282 sequences. (Running on oeis4.)