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 A066643 #20 Jan 31 2023 04:26:16
%S A066643 0,3,12,28,50,78,113,153,201,254,314,380,452,530,615,706,804,907,1017,
%T A066643 1134,1256,1385,1520,1661,1809,1963,2123,2290,2463,2642,2827,3019,
%U A066643 3216,3421,3631,3848,4071,4300,4536,4778,5026,5281,5541,5808,6082,6361,6647
%N A066643 a(n) = floor(Pi*n^2).
%H A066643 Harry J. Smith, <a href="/A066643/b066643.txt">Table of n, a(n) for n = 0..1000</a>
%F A066643 a(n) = floor(Pi*n^2).
%F A066643 a(n) = A022844(n^2) . - _R. J. Mathar_, Jan 25 2023
%t A066643 Table[ Floor[Pi*n^2], {n, 1, 50} ]
%o A066643 (PARI) { for (n=1, 1000, write("b066643.txt", n, " ", floor(Pi*n^2)) ) } \\ _Harry J. Smith_, Mar 15 2010
%Y A066643 Cf. A338020 (first differences).
%K A066643 easy,nonn
%O A066643 0,2
%A A066643 _Amarnath Murthy_, Dec 29 2001
%E A066643 Corrected and extended by _Robert G. Wilson v_, Jan 03 2002