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%I #13 Jun 29 2021 05:56:08
%S 2393,15497,18149,18617,20021,25819,26183,26339,29303,39937,42953,
%T 48491,52313,53327,57331,58189,59021,65183,81953,82499,87491,91703,
%U 98047,102233,104287,109097,111229,119419,129793,131171,143287,143833,162007
%N Primes p whose period of reciprocal equals (p-1)/13.
%H Amiram Eldar, <a href="/A098680/b098680.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, 15000]], f[ # ] == 13 &]
%Y Cf. A097443, A055628, A056157, A056210, A056211, A056212, A056213, A056214, A056215, A056216, A056217, A135073.
%K nonn,base
%O 1,1
%A _Robert G. Wilson v_, Sep 15 2004
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