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 A051221 #28 Apr 10 2025 19:37:36
%S A051221 0,1,6,9,10,19,36,39,51,64,75,84,91,96,99,100,144,159,199,216,271,324,
%T A051221 375,396,424,471,516,559,591,600,639,676,711,744,775,784,804,831,856,
%U A051221 879,900,919,936,951,964,975,984,991,996,999,1000,1164,1351,1404,1536,1719,1756,1900,1999
%N A051221 Numbers of the form 10^x-y^2 >= 0.
%C A051221 The values <= 2000 listed in this sequence are obtained from x <= 7. Seiichi Azuma proved that the list is complete up to 2000. - _Seiichi Azuma_, Apr 02 2025
%H A051221 Seiichi Azuma, <a href="https://arxiv.org/abs/2504.00116">Elementary Proof of the Completeness of OEIS A051221 Below 2000</a>, arXiv:2504.00116 [math.NT], 2025. See pp. 1, 4.
%t A051221 (* This program is unsafe and should not be used to extend the sequence. *)
%t A051221 max = 2000; Clear[f]; f[m_] := f[m] = Select[Table[10^x - y^2, {x, 0, m}, {y, 0, Ceiling[10^(x/2)]}] // Flatten // Union, 0 <= # <= max &]; f[1]; f[m = 2]; While[f[m] != f[m - 1], m++]; Print["m = ", m]; A051221 = f[m] (* _Jean-François Alcover_, May 13 2017 *)
%Y A051221 Cf. A128826.
%K A051221 nonn
%O A051221 1,3
%A A051221 _David W. Wilson_