A056215 Primes p whose reciprocal has period (p-1)/10.

281, 521, 1031, 1951, 2281, 2311, 2591, 3671, 5471, 5711, 6791, 7481, 8111, 8681, 8761, 9281, 9551, 10601, 11321, 12401, 13151, 13591, 14831, 14951, 15671, 16111, 16361, 18671, 21191, 21521, 21881, 24281, 24551, 25391, 25801, 25841, 26161

Offset: 1

Author

Robert G. Wilson v, Sep 15 2004

Keywords

• nonn
• base

Comments

Cyclic numbers of the tenth degree (or tenth order): the reciprocals of these numbers belong to one of ten different cycles. Each cycle has (p-1)/10 digits.

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000
• Index entries for sequences related to decimal expansion of 1/n

Crossrefs

Cf. A097443, A055628, A056157, A056210, A056211, A056212, A056213, A056214, A056216, A056217, A098680, A135073.

Programs

Mathematica

f[n_Integer] := Block[{ds = Divisors[n - 1]}, (n - 1)/Take[ ds, Position[ PowerMod[ 10, ds, n], 1] [[1, 1]]] [[ -1]]]; Select[ Prime[ Range[4, 3000]], f[ # ] == 10 &]

Extensions

Entry revised by N. J. A. Sloane, Apr 30 2007