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A102947 Numbers n such that 2*10^n-3 is prime. 2
1, 2, 3, 4, 13, 14, 76, 237, 872, 988, 1280, 1370, 2686, 3612, 4051, 4645, 9162, 10856, 25959, 64882, 144220, 153746, 185930 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that 10^n + 8*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

a(21) > 10^5. - Robert Price, Nov 16 2014

a(24) > 2*10^5. - Robert Price, Jul 11 2015

LINKS

Table of n, a(n) for n=1..23.

Makoto Kamada, Prime numbers of the form 199...997.

Index entries for primes involving repunits.

FORMULA

a(n) = A102034(n) + 1.

MATHEMATICA

Do[ If[ PrimeQ[2*10^n - 3], Print[n]], {n, 0, 10000}]

PROG

(PARI) is(n)=ispseudoprime(2*10^n-3) \\ Charles R Greathouse IV, Jun 06 2017

CROSSREFS

Cf. A102034.

Sequence in context: A303385 A325709 A126129 * A281512 A295396 A236440

Adjacent sequences:  A102944 A102945 A102946 * A102948 A102949 A102950

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Dec 16 2004

EXTENSIONS

Addition of a(18)-a(20) from Kamada data by Robert Price, Dec 09 2010

a(21)-a(23) from Robert Price, Jul 11 2015

STATUS

approved

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Last modified December 11 23:44 EST 2019. Contains 329945 sequences. (Running on oeis4.)