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 A104909 #6 Jun 28 2021 02:48:18
%S A104909 0,0,6,5,7,11,15,24,36,51,70,93,125,163,214,274,348,445,570,728,926,
%T A104909 1181,1505,1918,2440,3108,3954,5035,6403,8152,10366,13196,16788,21357,
%U A104909 27172,34562,43969,55928,71150,90509,115128,146446,186287,236964,301424,383419
%N A104909 a(n) = A104908(n) - 10*A104863(n).
%H A104909 G. C. Greubel, <a href="/A104909/b104909.txt">Table of n, a(n) for n = 1..1000</a>
%t A104909 A104863[n_]:= A104863[n]= If[n<3, 10*(2*n-1), Floor[Sqrt[A104863[n-1]^2 + A104863[n - 2]^2]]];
%t A104909 A104908[n_]:= A104908[n]= If[n<3, 100*(2*n-1), Floor[Sqrt[A104908[n-1]^2 + A104908[n-2]^2]]];
%t A104909 A104909[n_]:= A104908[n] -10*A104863[n];
%t A104909 Table[A104909[n], {n, 60}] (* _G. C. Greubel_, Jun 27 2021 *)
%Y A104909 Cf. A104803, A104908, A104910.
%K A104909 nonn
%O A104909 1,3
%A A104909 _Zak Seidov_, Mar 29 2005
%E A104909 Terms a(33) onward added by _G. C. Greubel_, Jun 27 2021