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 A077770 #8 Feb 16 2025 08:32:48
%S A077770 0,4,12,16,20,28,32,44,52,52,56,60,76,80,84,84,92,104,116,116,112,140,
%T A077770 132,136,148,148,164,160,164,180,176,204,196,204,216,196,228,216,252,
%U A077770 236,224,260,260,284,272,260,292,288,308,300,316,312,300,332,320,364
%N A077770 Number of ordered pairs of integers (x,y) with n^2 < x^2 + y^2 < (n+1)^2; number of lattice points between circles of radii n and n+1.
%C A077770 Note that 2*A077768(n)-a(n)/4 is the characteristic sequence for the Beatty sequence A001951(n).
%H A077770 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/GausssCircleProblem.html">Gauss's Circle Problem</a>
%F A077770 a(n) = A051132(n+1) - A000328(n)
%t A077770 Table[Sum[SquaresR[2, k], {k, n^2 + 1, (n + 1)^2 - 1}], {n, 0, 100}]
%Y A077770 Cf. A000328, A001951, A051132, A077768.
%K A077770 nonn
%O A077770 0,2
%A A077770 _T. D. Noe_, Nov 20 2002