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 A209899 #12 Aug 03 2014 14:01:40
%S A209899 0,0,0,0,0,0,0,0,1,1,1,1,1,1,1,2,2,2,2,2,2,2,2,3,3,3,3,3,3,3,4,4,4,4,
%T A209899 4,4,4,5,5,5,5,5,5,5,5,6,6,6,6,6,6,6,7,7,7,7,7,7,7,7,8,8,8,8,8,8,8,9,
%U A209899 9,9,9,9,9,9,10,10,10,10,10,10,10,10,11,11
%N A209899 Floor of the expected number of empty cells in a random placement of 2n balls into n cells.
%D A209899 W. Feller, An Introduction to Probability Theory and its Applications, 2nd ed, Wiley, New York, 1965, p. 226.
%F A209899 a(n) = floor(n*(1-1/n)^(2n)).
%t A209899 Table[Floor[n*(1 - 1/n)^(2 n)], {n, 100}] (* _T. D. Noe_, Mar 15 2012 *)
%Y A209899 Cf. A209900.
%K A209899 nonn
%O A209899 1,16
%A A209899 _Washington Bomfim_, Mar 14 2012