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 A133296 #19 Mar 17 2025 22:22:20
%S A133296 0,2,4,6,8,19,39,59,79,99,299,499,699,899,1999,3999,5999,7999,9999,
%T A133296 29999,49999,69999,89999,199999,399999,599999,799999,999999,2999999,
%U A133296 4999999,6999999,8999999,19999999,39999999,59999999,79999999,99999999,299999999,499999999
%N A133296 Smallest number whose sum of digits is 2n.
%H A133296 <a href="/index/Rec#order_10">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,0,0,0,0,0,100,-100).
%F A133296 From _Alois P. Heinz_, Mar 12 2025: (Start)
%F A133296 G.f.: x*(20*x^8+20*x^7+20*x^6+20*x^5+11*x^4+2*x^3+2*x^2+2*x+2)/((x-1)*(100*x^9-1)).
%F A133296 a(n) = A051885(2*n). (End)
%p A133296 a:= n-> parse(cat(irem(2*n, 9, 'r'), 9$r)):
%p A133296 seq(a(n), n=0..38); # _Alois P. Heinz_, Mar 12 2025
%t A133296 a[n_] := (Mod[2n, 9] + 1)*10^Floor[2n/9] - 1; Table[a[n], {n, 0,38}] (* _James C. McMahon_, Mar 13 2025 *)
%Y A133296 Bisection of A051885 (even part).
%Y A133296 Cf. A131668.
%K A133296 nonn,base,easy
%O A133296 0,2
%A A133296 _Paul Curtz_, Oct 17 2007