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 A304651 #25 Aug 02 2023 05:21:06
%S A304651 0,4,8,8,8,16,16,16,16,16,24,24,24,32,32,32,32,40,40,40,40,40,40,40,
%T A304651 40,48,56,56,56,64,64,64,64,64,72,72,72,80,80,80,80,88,88,88,88,88,88,
%U A304651 88,88,88,96,96,96,104,104,104,104,104,112,112,112,120,120,120,120
%N A304651 Number of coprime pairs (x,y) with x^2 + y^2 <= n.
%H A304651 Seiichi Manyama, <a href="/A304651/b304651.txt">Table of n, a(n) for n = 0..10000</a>
%F A304651 a(n) = a(n-1) + 4*A000089(n) for n > 0.
%e A304651 a(2) = 8 counts (x,y) = (-1,-1), (-1,0), (-1,1), (0,-1), (0,1), (1,-1), (1,0) and (1,1).
%t A304651 a89[n_] := a89[n] = Product[{p, e} = pe; Which[p < 3 && e == 1, 1, p == 2 && e > 1, 0, Mod[p, 4] == 1, 2, Mod[p, 4] == 3, 0, True, a89[p^e]], {pe, FactorInteger[n]}];
%t A304651 a[n_] := a[n] = If[n == 0, 0, a[n-1] + 4 a89[n]];
%t A304651 Table[a[n], {n, 0, 100}] (* _Jean-François Alcover_, Aug 02 2023 *)
%Y A304651 Cf. A000089, A175341, A305117.
%K A304651 nonn
%O A304651 0,2
%A A304651 _Seiichi Manyama_, May 26 2018