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 A339273 #38 Apr 23 2021 13:51:10
%S A339273 8,20,32,40,52,68,72,80,100,104,116,128,136,148,160,164,180,200,208,
%T A339273 212,232,244,260,272,288,292,296,320,328,340,356,360,388,392,400,404,
%U A339273 416,424,436,452,464,468,488,500,512,520,544,548,580,584,592,596,612,628,640,648,656
%N A339273 Sums of two nonzero even squares.
%F A339273 a(n) = 4*A000404(n).
%F A339273 Characteristic function: sign(Sum_{k=1..floor(n/2)} ((k+1) mod 2) * ((n-k+1) mod 2) * c(k) * c(n-k)), where c is the characteristic function of squares (A010052).
%e A339273 20 is in the sequence since it is the sum of two nonzero even squares, 2^2 + 4^2 = 4 + 16 = 20.
%t A339273 Table[If[Sum[Mod[i + 1, 2] Mod[n - i + 1, 2] (Floor[Sqrt[i]] - Floor[Sqrt[i - 1]]) (Floor[Sqrt[n - i]] - Floor[Sqrt[n - i - 1]]), {i, Floor[n/2]}] > 0, n, {}], {n, 700}] // Flatten
%Y A339273 Cf. A000404, A010052, A057653, A097269.
%K A339273 nonn,easy
%O A339273 1,1
%A A339273 _Wesley Ivan Hurt_, Dec 24 2020