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%I #16 Jun 29 2021 05:55:22
%S 73,1423,1459,2377,2503,3457,7741,9433,10891,10909,16057,17299,17623,
%T 20269,21313,22699,24103,26263,28621,28927,29629,30817,32257,34273,
%U 34327,35461,35731,36343,36793,37549,37567,37657,38737,39367,39979
%N Primes p whose period of reciprocal equals (p-1)/9.
%C Cyclic numbers of the ninth degree (or ninth order): the reciprocals of these numbers belong to one of nine different cycles. Each cycle has the (number minus 1)/9 digits.
%H Amiram Eldar, <a href="/A056214/b056214.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, 5000]], f[ # ] == 9 &]
%Y Cf. A097443, A055628, A056157, A056210, A056211, A056212, A056213, 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