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%I #17 Jun 29 2021 05:55:05
%S 211,617,1499,2087,2857,6007,6469,7127,7211,7589,9661,10193,13259,
%T 13553,14771,18047,18257,19937,20903,21379,23549,26153,27259,27539,
%U 32299,33181,33461,34847,35491,35897,41651,42407,42491,43051,43793
%N Primes p whose period of reciprocal equals (p-1)/7.
%C Cyclic numbers of the seventh degree (or seventh order): the reciprocals of these numbers belong to one of seven different cycles. Each cycle has the (number minus 1)/7 digits.
%H Amiram Eldar, <a href="/A056212/b056212.txt">Table of n, a(n) for n = 1..10000</a>
%H <a href="/index/1#1overn">Index entries for sequences related to decimal expansion of 1/n</a>
%t 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, 4700]], f[ # ] == 7 &]
%Y Cf. A097443, A055628, A056157, A056210, A056211, A056213, A056214, A056215, A056216, A056217, A098680, A135073.
%K nonn,base
%O 1,1
%A _Robert G. Wilson v_, Aug 02 2000
%E Edited by _N. J. A. Sloane_, Apr 30 2007