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 A348466 #6 Oct 21 2021 01:03:29
%S A348466 1,10,109,109108,109108109107,109108109107109108109106,
%T A348466 109108109107109108109106109108109107109108109105,
%U A348466 109108109107109108109106109108109107109108109105109108109107109108109106109108109107109108109104
%N A348466 a(0)=1; for n >= 0, a(n+1) is the concatenation of a(n) and a(n)-1.
%t A348466 Nest[Append[#1, #2*10^IntegerLength[#3] + #3] & @@ {#, #[[-1]], #[[-1]] - 1} &, {1, 10}, 6] (* _Michael De Vlieger_, Oct 20 2021 *)
%Y A348466 Suggested by A033564.
%K A348466 nonn,base
%O A348466 0,2
%A A348466 _N. J. A. Sloane_, Oct 20 2021