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 A043525 #26 Sep 19 2021 12:18:50
%S A043525 9,19,29,39,49,59,69,79,89,90,91,92,93,94,95,96,97,98,109,119,129,139,
%T A043525 149,159,169,179,189,190,191,192,193,194,195,196,197,198,209,219,229,
%U A043525 239,249,259,269,279,289,290,291,292,293,294,295,296,297,298,309,319
%N A043525 Numbers having one 9 in base 10.
%H A043525 Enrique Pérez Herrero, <a href="/A043525/b043525.txt">Table of n, a(n) for n = 1..2000</a>
%H A043525 <a href="/index/Ar#10-automatic">Index entries for 10-automatic sequences</a>.
%F A043525 Sum_{n>=1} 1/a(n) = A140502. - _Amiram Eldar_, Nov 14 2020
%t A043525 Select[Range[300],DigitCount[#,10,9]==1&] (* _Harvey P. Dale_, Jan 19 2013 *)
%o A043525 (Python)
%o A043525 def ok(n): return str(n).count('9') == 1
%o A043525 print(list(filter(ok, range(320)))) # _Michael S. Branicky_, Sep 19 2021
%Y A043525 Cf. A043489, A043493, A043497, A043501, A043505, A043509, A043513, A043517, A043521.
%Y A043525 Cf. A011539, A140502.
%Y A043525 Subsequence of A011539.
%K A043525 nonn,base
%O A043525 1,1
%A A043525 _Clark Kimberling_