A093172 Primes of the form 10^n - 3.

7, 97, 997, 99999999999999997

Offset: 1

Author

Rick L. Shepherd, Mar 26 2004

Keywords

• nonn

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

• Makoto Kamada, Prime numbers of the form 99...997.
• Index entries for primes involving repunits

Crossrefs

Subsequence of A020471 and hence of A030096.

Cf. A002275, A056662, A089675.

Programs

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 *)

PARI

for(n=1,9, if(isprime(p=10^n-3), print1(p", "))) \\ Charles R Greathouse IV, Dec 13 2024

Extensions

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