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 A235532 #14 Jun 22 2020 12:56:11 %S A235532 0,0,3,7,13,21,30,42,54,69,85,103,123,145,168,193,219,248,278,309,343, %T A235532 378,415,454,494,536,580,625,672,721,772,824,879,934,992,1051,1112, %U A235532 1175,1239,1305,1373,1442,1514,1587,1661,1738,1816,1896,1977,2061,2146,2232,2321 %N A235532 a(n) = floor(n^2 * (4-Pi)). %C A235532 a(n) = floor(As(n) - Ac(n)), where Ac(n) is the area of the circle of radius n, and As(n) is the area of square with side length 2n. %t A235532 Floor[(4-Pi)#^2]&/@Range[0,60] (* _Harvey P. Dale_, Jan 10 2020 *) %o A235532 (Python) %o A235532 import math %o A235532 for n in range(77): print(str(int(n*n*(4-math.pi))), end=',') %Y A235532 Cf. A066643, A057672, A000290. %K A235532 nonn %O A235532 0,3 %A A235532 _Alex Ratushnyak_, Jan 11 2014