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 A302861 #9 Feb 16 2025 08:33:53
%S A302861 1,3,13,123,1281,16875,252673,4031123,70554353,1318315075,26107328109,
%T A302861 549772933959,12147113355505,280978137279483,6780378828922333,
%U A302861 169829490474843659,4409771551548703649,118361723203178140163,3277041835527134201777,93455465161026267454527
%N A302861 a(n) = [x^(n^2)] theta_3(x)^n/(1 - x), where theta_3() is the Jacobi theta function.
%C A302861 a(n) = number of integer lattice points inside the n-dimensional hypersphere of radius n.
%H A302861 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/JacobiThetaFunctions.html">Jacobi Theta Functions</a>
%H A302861 <a href="/index/Su#ssq">Index entries for sequences related to sums of squares</a>
%F A302861 a(n) = A122510(n,n^2).
%t A302861 Table[SeriesCoefficient[EllipticTheta[3, 0, x]^n/(1 - x), {x, 0, n^2}], {n, 0, 19}]
%t A302861 Table[SeriesCoefficient[1/(1 - x) Sum[x^k^2, {k, -n, n}]^n, {x, 0, n^2}], {n, 0, 19}]
%Y A302861 Main diagonal of A302997.
%Y A302861 Cf. A000122, A000328, A000605, A055410, A055411, A055412, A055413, A055414, A055415, A055416, A122510, A232173, A302860.
%K A302861 nonn
%O A302861 0,2
%A A302861 _Ilya Gutkovskiy_, Apr 14 2018