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A093947 Primes of the form 8*10^n - 1. 0
7, 79, 79999, 799999, 799999999, 79999999999, 79999999999999999999999999, 79999999999999999999999999999999999999999999999999, 79999999999999999999999999999999999999999999999999999999999999999999999999999 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Equivalently, primes of the form 7*10^n + 9*R_n, where R_n is the repunit (A002275) of length n.

LINKS

Table of n, a(n) for n=1..9.

Makoto Kamada, Prime numbers of the form 799...99.

Index entries for primes involving repunits.

MATHEMATICA

Select[Table[FromDigits[PadRight[{7}, n, 9]], {n, 50}], PrimeQ] (* Vincenzo Librandi, May 08 2019 *)

PROG

(MAGMA) [a: n in [0..200] | IsPrime(a) where a is (8*10^n-1)]; // Vincenzo Librandi, May 08 2019

CROSSREFS

Cf. A056721 (corresponding n).

Sequence in context: A267798 A201704 A052385 * A222137 A115986 A295843

Adjacent sequences:  A093944 A093945 A093946 * A093948 A093949 A093950

KEYWORD

nonn

AUTHOR

Rick L. Shepherd, Apr 17 2004

STATUS

approved

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Last modified October 15 12:31 EDT 2019. Contains 328026 sequences. (Running on oeis4.)