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 A056213 #14 Apr 02 2018 21:04:17
%S A056213 41,241,1601,1609,2441,2969,3041,3449,3929,4001,4409,5009,6089,6521,
%T A056213 6841,8161,8329,8609,9001,9041,9929,13001,13241,14081,14929,16001,
%U A056213 16481,17489,17881,18121,19001,20249,20641,20921,21529,22481,23801
%N A056213 Primes p for which the period of reciprocal = (p-1)/8.
%C A056213 Cyclic numbers of the eighth degree (or eighth order): the reciprocals of these numbers belong to one of eight different cycles. Each cycle has the (number minus 1)/8 digits.
%C A056213 From _Robert Israel_, Apr 02 2018: (Start)
%C A056213 Primes p such that A002371(A000720(p))=(p-1)/8.
%C A056213 All terms == 1 (mod 8). (End)
%H A056213 Robert Israel, <a href="/A056213/b056213.txt">Table of n, a(n) for n = 1..10000</a>
%H A056213 <a href="/index/1#1overn">Index entries for sequences related to decimal expansion of 1/n</a>
%p A056213 select(t -> isprime(t) and numtheory:-order(10, t) = (t-1)/8, [seq(t,t=17..24000,8)]); # _Robert Israel_, Apr 02 2018
%t A056213 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, 2700]], f[ # ] == 8 &]
%K A056213 nonn,base
%O A056213 1,1
%A A056213 _Robert G. Wilson v_, Aug 02 2000
%E A056213 Edited by _N. J. A. Sloane_, Apr 30 2007