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URL: https://oeis.org/A093177

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A093177
Primes of the form 90*R_k + 1, where R_k is the repunit (A002275) of length k.
10
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
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
KEYWORD
nonn
AUTHOR
Rick L. Shepherd, Mar 27 2004
EXTENSIONS
Edited by Ray Chandler, Feb 26 2012
STATUS
approved