

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^n1)]; // Vincenzo Librandi, May 08 2019


CROSSREFS

Cf. A056721 (corresponding n).
Sequence in context: A201704 A331424 A052385 * A222137 A115986 A295843
Adjacent sequences: A093944 A093945 A093946 * A093948 A093949 A093950


KEYWORD

nonn


AUTHOR

Rick L. Shepherd, Apr 17 2004


STATUS

approved



