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