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 A128020 #9 Oct 10 2019 11:22:24
%S A128020 1,2,6,12,25,48,98,200,396,790,1584,3168,6331,12670,25335,50672,
%T A128020 101354,202698,405403,810800,1621599,3243196,6486391,12972792,
%U A128020 25945575,51891164,103782330,207564644,415129287,830258580,1660517170,3321034336
%N A128020 a(n) = the multiple of n which is > (sum{k=1 to n-1} a(k)) and is <= (n + sum{k=1 to n-1} a(k)).
%F A128020 a(n) = n * (1+ floor(sum{k=1 to n-1} a(k) /n)).
%t A128020 f[l_List] := Block[{n = Length[l] + 1},Append[l, n*(1 + Floor[Plus @@ l/n])]];Nest[f, {}, 33] (* _Ray Chandler_, Feb 12 2007 *)
%Y A128020 Cf. A128021, A128022.
%K A128020 easy,nonn
%O A128020 1,2
%A A128020 _Leroy Quet_, Feb 11 2007
%E A128020 Extended by _Ray Chandler_, Feb 12 2007