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 A218127 #14 Apr 15 2021 13:05:56
%S A218127 1,10,90,990,9900,99990,998910,9999990,99990000,999999000,9999899910,
%T A218127 99999999990,999998990100,9999999999990,99999989999910,
%U A218127 999999999899010,9999999900000000,99999999999999990,999999998999001000,9999999999999999990,99999999989999990100
%N A218127 Number of 10-ary sequences with primitive period n.
%H A218127 Seiichi Manyama, <a href="/A218127/b218127.txt">Table of n, a(n) for n = 0..1000</a> (terms 0..300 from Alois P. Heinz)
%F A218127 a(n) = Sum_{d|n} 10^d * mu(n/d) for n>0, a(0) = 1.
%F A218127 G.f.: 1 + 10 * Sum_{k>=1} mu(k) * x^k / (1 - 10*x^k). - _Ilya Gutkovskiy_, Apr 15 2021
%p A218127 with(numtheory):
%p A218127 a:= n-> `if`(n=0, 1, add(10^d*mobius(n/d), d=divisors(n))):
%p A218127 seq(a(n), n=0..30);
%Y A218127 Column k=10 of A143324.
%K A218127 nonn
%O A218127 0,2
%A A218127 _Alois P. Heinz_, Oct 21 2012