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 A218124 #11 Apr 14 2021 22:25:37
%S A218124 1,7,42,336,2352,16800,117264,823536,5762400,40353264,282458400,
%T A218124 1977326736,13841167200,96889010400,678222249264,4747561492800,
%U A218124 33232924804800,232630513987200,1628413557439536,11398895185373136,79792266015134400,558545864082460128
%N A218124 Number of 7-ary sequences with primitive period n.
%H A218124 Alois P. Heinz, <a href="/A218124/b218124.txt">Table of n, a(n) for n = 0..400</a>
%F A218124 a(n) = Sum_{d|n} 7^d * mu(n/d) for n>0, a(0) = 1.
%F A218124 G.f.: 1 + 7 * Sum_{k>=1} mu(k) * x^k / (1 - 7*x^k). - _Ilya Gutkovskiy_, Apr 14 2021
%p A218124 with(numtheory):
%p A218124 a:= n-> `if`(n=0, 1, add(7^d *mobius(n/d), d=divisors(n))):
%p A218124 seq(a(n), n=0..30);
%Y A218124 Column k=7 of A143324.
%K A218124 nonn
%O A218124 0,2
%A A218124 _Alois P. Heinz_, Oct 21 2012