A093177 Primes of the form 90*R_k + 1, where R_k is the repunit (A002275) of length k.

991, 99991, 9999991, 999999999999999999999999999999991, 999999999999999999999999999999999999999999991, 999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999991

Offset

1,1

Comments

Primes of the form 10^k - 9 (k=3,5,7,...). - Vincenzo Librandi, Nov 16 2010

Links

Table of n, a(n) for n=1..6.

Makoto Kamada, Prime numbers of the form 99...991.

Index entries for primes involving repunits

Formula

a(n) = 10^(A056696(n)+1) - 9 = 10^A095714(n) - 9.

Crossrefs

Cf. A056696 (corresponding k), A095714.

Sequence in context: A137703 A255098 A155509 * A161926 A172698 A109149

Adjacent sequences: A093174 A093175 A093176 * A093178 A093179 A093180

Keyword

nonn

Author

Rick L. Shepherd, Mar 27 2004

Extensions

Edited by Ray Chandler, Feb 26 2012

Status

approved