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 A053456 #12 Mar 23 2022 12:17:03 %S A053456 0,1,1,9,9,21,25,37,45,69,69,97,109,137,145,177,193,225,249,293,305, %T A053456 349,373,421,437,489,517,577,609,665,697,749,793,861,889,973,1005, %U A053456 1085,1125,1201,1245,1313,1369,1457,1513,1597,1649,1741,1789,1885,1941 %N A053456 Open disk numbers (version 1): a(n) is the number of points (i,j), i,j, integers, contained in an open disk of diameter n, centered at (0,0). %F A053456 a(n)/(n/2)^2->Pi. %Y A053456 Cf. A053411, A053457, A053458, A053459. %Y A053456 Bisections: A051132, A036704. %Y A053456 Cf. A000796 (Pi). %K A053456 easy,nonn %O A053456 0,4 %A A053456 Klaus Strassburger (strass(AT)ddfi.uni-duesseldorf.de), Jan 13 2000