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 A162676 #11 Dec 23 2016 17:39:39
%S A162676 1,4,48,956,26490,937342,40291608,2036155284,118202408622,
%T A162676 7747410899954,565695467415936,45525704815717568,4002930269944724664,
%U A162676 381750656962687053108,39244733577786624617904,4325973539461955182836900,508971415418900757219557142
%N A162676 Number of different fixed (possibly) disconnected n-ominoes bounded (not necessarily tightly) by an n*n square.
%F A162676 a(n) = binomial(n^2,n)-2*binomial((n-1)*n,n)+binomial((n-1)^2,n).
%e A162676 a(2)=4: the two rotations of the (connected) domino and the two rotations of the disconnected domino consisting of two squares connected at a vertex.
%t A162676 Table[Binomial[n^2,n]-2*Binomial[(n-1)n,n]+Binomial[(n-1)^2,n],{n,20}] (* _Harvey P. Dale_, Oct 01 2013 *)
%o A162676 (PARI) a(n) = binomial(n^2,n) - 2*binomial((n-1)*n,n) + binomial((n-1)^2,n); \\ _Michel Marcus_, Aug 30 2013
%Y A162676 Cf. A162673, A162674, A162675, A162677.
%K A162676 nonn
%O A162676 1,2
%A A162676 _David Bevan_, Jul 27 2009