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A093947
Primes of the form 8*10^n - 1.
0
7, 79, 79999, 799999, 799999999, 79999999999, 79999999999999999999999999, 79999999999999999999999999999999999999999999999999, 79999999999999999999999999999999999999999999999999999999999999999999999999999
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.
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: A201704 A331424 A052385 * A222137 A115986 A295843
KEYWORD
nonn
AUTHOR
Rick L. Shepherd, Apr 17 2004
STATUS
approved