%I A098680
%S A098680 2393,15497,18149,18617,20021,25819,26183,26339,29303,39937,42953,48491,
%T A098680 52313,53327,57331,58189,59021,65183,81953,82499,87491,91703,98047,
%U A098680 102233,104287,109097,111229,119419,129793,131171,143287,143833,162007
%N A098680 Primes p for which the period of reciprocal = (p-1)/13.
%H A098680 <a href="Sindx_1.html#1overn">Index entries for sequences related to 
               decimal expansion of 1/n</a>
%t A098680 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 A098680 Sequence in context: A020394 A020428 A100974 this_sequence A115931 A108055 
               A043420
%Y A098680 Adjacent sequences: A098677 A098678 A098679 this_sequence A098681 A098682 
               A098683
%K A098680 nonn
%O A098680 1,1
%A A098680 Robert G. Wilson v (rgwv(AT)rgwv.com), Sep 15 2004