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 A004728 #19 Apr 22 2021 22:10:04
%S A004728 0,1,2,3,4,5,6,7,8,10,11,12,13,14,15,16,17,18,1,20,21,22,23,24,25,26,
%T A004728 27,28,2,30,31,32,33,34,35,36,37,38,3,40,41,42,43,44,45,46,47,48,4,50,
%U A004728 51,52,53,54,55,56,57,58,5,60,61,62,63,64,65,66,67,68,6,70,71
%N A004728 Delete all 9's from the sequence of nonnegative integers.
%t A004728 Join[{0},Table[FromDigits[IntegerDigits[n]/.(9->Nothing)],{n,90}]/.(0-> Nothing)] (* _Harvey P. Dale_, Aug 10 2019 *)
%o A004728 (Python)
%o A004728 def A004728(n):
%o A004728 l = len(str(n))
%o A004728 m = 10**l-1
%o A004728 k = n + l - int(n+l < m)
%o A004728 return 8 if k == m else int(str(k).replace('9','')) # _Chai Wah Wu_, Apr 20 2021
%Y A004728 Cf. A004719, A004720, A004721, A004722, A004723, A004724, A004725, A004726, A004727.
%K A004728 base,nonn
%O A004728 0,3
%A A004728 _N. J. A. Sloane_