A056694 - OEIS

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A056694

Numbers k such that 80*R_k + 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

2

0, 1, 2, 4, 7, 8, 14, 50, 70, 76, 223, 295, 314, 2089, 2905, 3394, 3881, 5113, 6055, 7253, 7994, 18172, 18970, 35005, 69673

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OFFSET

1,3

COMMENTS

Also numbers k such that (8*10^(k+1)-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) = A099422(n) - 1. [adapted by Georg Fischer, Jan 04 2021]

MATHEMATICA

Do[ If[ PrimeQ[80*(10^n - 1)/9 + 3], Print[n]], {n, 0, 5000}]

PROG

(Magma) [n: n in [0..500] | IsPrime((8*10^(n+1)-53) div 9)]; // Vincenzo Librandi, Nov 01 2014

CROSSREFS

Cf. A002275, A093166, A099422.

Sequence in context: A015893 A018430 A018265 * A090606 A241548 A373801

Adjacent sequences: A056691 A056692 A056693 * A056695 A056696 A056697

KEYWORD

hard,nonn

AUTHOR

Robert G. Wilson v, Aug 10 2000

EXTENSIONS

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

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

STATUS

approved