A093948 Primes of the form 9*10^k - 1.

89, 8999, 89999999, 89999999999999999999, 899999999999999999999999999999, 89999999999999999999999999999999999999, 8999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999

Offset: 1

Author

Rick L. Shepherd, Apr 17 2004

Keywords

• nonn

Comments

Equivalently, primes of the form 8*10^k + 9*R_k, where R_k is the repunit (A002275) of length k.

Links

• Makoto Kamada, Prime numbers of the form 899...999.
• Index entries for primes involving repunits.

Crossrefs

Cf. A002275, A056725 (corresponding k).

Primes in A109002.

Formula

a(n) = 9*10^A056725(n) - 1 = A109002(A056725(n) + 1). - Elmo R. Oliveira, Jun 14 2025