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A093172 Primes of the form 10^n - 3. 2
7, 97, 997, 99999999999999997 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Primes of the form (9*10^n - 27)/9. - Vincenzo Librandi, Nov 16 2010

Also primes of the form 9*R_n - 2, where R_n is the repunit (A002275) of length n.

The next term has 140 digits.

a(n) = 10^A089675(n) - 3 = 10^(A056662(n) + 1) - 3. - Farideh Firoozbakht, Nov 27 2013

LINKS

Table of n, a(n) for n=1..4.

Makoto Kamada, Prime numbers of the form 99...997.

Index entries for primes involving repunits

MATHEMATICA

Do[If[PrimeQ[10^n - 3], Print[10^n - 3]], {n, 100}] (* Farideh Firoozbakht, Nov 27 2013 *)

Select[Table[FromDigits[PadLeft[{7}, n, 9]], {n, 25}], PrimeQ] (* Harvey P. Dale, Dec 12 2020 *)

CROSSREFS

Cf. A002275, A056662, A089675.

Sequence in context: A158579 A003618 A173833 * A074110 A155644 A243867

Adjacent sequences:  A093169 A093170 A093171 * A093173 A093174 A093175

KEYWORD

nonn

AUTHOR

Rick L. Shepherd, Mar 26 2004

EXTENSIONS

Name shortened and old name moved to comments by Alex Ratushnyak, Apr 26 2012

STATUS

approved

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Last modified April 22 06:01 EDT 2021. Contains 343161 sequences. (Running on oeis4.)