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A099422 Numbers k such that 8*R_k - 5 is prime, where R_k = 11...1 is the repunit (A002275) of length k. 3
1, 2, 3, 5, 8, 9, 15, 51, 71, 77, 224, 296, 315, 2090, 2906, 3395, 3882, 5114, 6056, 7254, 7995, 18173, 18971, 35006, 69674 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also numbers k >= 1 such that (8*10^k - 53)/9 is prime.

a(26) > 10^5. - Robert Price, Oct 31 2014

LINKS

Table of n, a(n) for n=1..25.

Makoto Kamada, Prime numbers of the form 88...883.

Index entries for primes involving repunits

FORMULA

a(n) = A056694(n) + 1.

MATHEMATICA

Do[ If[ PrimeQ[ 8(10^n - 1)/9 - 5], Print[n]], {n, 1, 5000}]

PROG

(MAGMA) [n: n in [1..500] | IsPrime((8*10^n-53) div 9)]; // Vincenzo Librandi, Nov 01 2014

CROSSREFS

Cf. A002275, A056664, A056694, A093166.

Sequence in context: A168154 A278334 A120057 * A294913 A056903 A229139

Adjacent sequences:  A099419 A099420 A099421 * A099423 A099424 A099425

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Oct 14 2004

EXTENSIONS

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

a(22)-a(25) from Robert Price, Oct 31 2014

a(1)=0 removed by Georg Fischer, Jan 03 2021

STATUS

approved

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Last modified September 26 16:08 EDT 2021. Contains 347669 sequences. (Running on oeis4.)