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 A162677 #6 Aug 30 2013 10:57:49 %S A162677 1,10,400,57856,31522816,66605547520,554222579875840, %T A162677 18303191835587117056,2408425353007592768536576, %U A162677 1265177138001297870205254369280,2655861110791164560222750369099284480 %N A162677 Number of different fixed (possibly) disconnected polyominoes (of any area) bounded (not necessarily tightly) by an n*n square. %F A162677 a(n) = 2^(n^2)-2*2^((n-1)*n)+2^((n-1)^2). %e A162677 a(2)=10: the monomino, 4 dominoes (2 strictly disconnected), 4 rotations of the L tromino, and the square tetromino. %o A162677 (PARI) a(n) = 2^(n^2) - 2*2^((n-1)*n) + 2^((n-1)^2); \\ _Michel Marcus_, Aug 30 2013 %Y A162677 Cf. A162673, A162674, A162675, A162676. %K A162677 nonn %O A162677 1,2 %A A162677 _David Bevan_, Jul 27 2009