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 A271990 #5 Jan 11 2020 15:57:47
%S A271990 9,27,63,92,127,168,215,267,325,389,459,535,617,705,799,898,1003,1114,
%T A271990 1231,1354,1483,1618,1759,1906,2059,2218,2383,2554,2731,2914,3103,
%U A271990 3297,3497,3703,3915,4133,4357,4587,4823,5065,5313,5567,5827,6093,6365,6643
%N A271990 g_n(9) where g is the weak Goodstein function defined in A266202.
%C A271990 For more info see A266201-A266202.
%t A271990 g[k_, n_] := If[k == 0, n, Total@ Flatten@ MapIndexed[#1 (k + 2)^(#2 - 1) &, Reverse@ IntegerDigits[#, k + 1]] &@ g[k - 1, n] - 1]; Table[g[n, 9], {n, 0, 45}]
%Y A271990 Cf. A271556: G_n(9).
%Y A271990 Weak Goodstein sequences: A137411: g_n(11); A265034: g_n(266); A267647: g_n(4); A267648: g_n(5); A271987: g_n(6); A266202: g_n(n); A266203: a(n)=k such that g_k(n)=0;
%K A271990 nonn,fini
%O A271990 0,1
%A A271990 _Natan Arie Consigli_, May 22 2016