This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A098680 #13 Jun 29 2021 05:56:08
%S A098680 2393,15497,18149,18617,20021,25819,26183,26339,29303,39937,42953,
%T A098680 48491,52313,53327,57331,58189,59021,65183,81953,82499,87491,91703,
%U A098680 98047,102233,104287,109097,111229,119419,129793,131171,143287,143833,162007
%N A098680 Primes p whose period of reciprocal equals (p-1)/13.
%H A098680 Amiram Eldar, <a href="/A098680/b098680.txt">Table of n, a(n) for n = 1..10000</a>
%H A098680 <a href="/index/1#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 Cf. A097443, A055628, A056157, A056210, A056211, A056212, A056213, A056214, A056215, A056216, A056217, A135073.
%K A098680 nonn,base
%O A098680 1,1
%A A098680 _Robert G. Wilson v_, Sep 15 2004