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 A101564 #10 Oct 01 2018 03:30:02
%S A101564 1,9,99,991,9999,100091,1000001,9999009,100000099,1000009991,
%T A101564 10000000001,100000099109,1000000000001,9999999000009,100000000010099,
%U A101564 999999990000991,9999999999999999,100000000100100091
%N A101564 a(n) = Sum_{k=0..n} (-1)^A010060(n-k)*[(n+1) mod (k+1) = 0]*10^k, where [] denotes the Iverson bracket.
%o A101564 (PARI) tm(n) = hammingweight(n)%2;
%o A101564 a(n) = sum(k=0, n, if (((n+1) % (k+1))==0, (-1)^tm(n-k)*10^k)); \\ _Michel Marcus_, Oct 01 2018
%Y A101564 Cf. A010060, A101563, A051731.
%K A101564 easy,nonn
%O A101564 0,2
%A A101564 _Paul Barry_, Dec 07 2004