A104381 Numbers k such that 10^(k-1) == 1 (mod k).

1, 3, 7, 9, 11, 13, 17, 19, 23, 29, 31, 33, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 91, 97, 99, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 259, 263

Offset

1,2

Comments

Superset of the full reptend primes.

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Eric Weisstein's World of Mathematics, Full Reptend Prime.

Mathematica

Select[ Range[270], Mod[ PowerMod[10, # - 1, # ] - 1, # ] == 0 &] (* Robert G. Wilson v, Mar 16 2005 *)
Join[{1}, Select[Range[300], PowerMod[10, #-1, #]==1&]] (* Harvey P. Dale, Oct 24 2016 *)

Prog

(PARI) isok(n) = lift(Mod(10, n)^(n-1)) == 1; \\ Michel Marcus, Sep 25 2014

Crossrefs

Cf. A005939.

Sequence in context: A105585 A080903 A172253 * A136333 A134454 A324695

Adjacent sequences: A104378 A104379 A104380 * A104382 A104383 A104384

Keyword

nonn

Author

Eric W. Weisstein, Mar 03 2005

Status

approved