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 A005650 M2704 #31 Oct 03 2017 01:31:23
%S A005650 1,1,3,7,47,207,2249,14501,216273,1830449,34662523,362983263,
%T A005650 8330310559,103938238111,2801976629841,40574514114061,
%U A005650 1256354802202337,20708839411614753,724160187180691379,13386284447024070647
%N A005650 Number of "magic squares" of order n (see comment line for exact definition).
%C A005650 This is the number of n X n square arrays with nonnegative integer entries in which every row and column add to 2 (A000681) normalized by dividing by n!/2^floor(n/2).
%D A005650 L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 125, #25, A_n.
%D A005650 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A005650 Vincenzo Librandi, <a href="/A005650/b005650.txt">Table of n, a(n) for n = 0..200</a>
%H A005650 <a href="/index/Mag#magic">Index entries for sequences related to magic squares</a>
%F A005650 a(n) = A000681(n)*2^floor(n/2)/n!.
%F A005650 a(n) ~ 2^(floor(n/2) + 1/2) * n^n * exp(1/2-n). - _Vaclav Kotesovec_, Aug 13 2013
%F A005650 Recurrence: a(n) = (2*n^2 - 4*n + 1)*a(n-2) - (n-3)*n*a(n-4). - _Vaclav Kotesovec_, Aug 13 2013
%t A005650 A000681[n_] := Sum[((2*i)!*n!^2)/(2^i*(i!^2*(n - i)!)), {i, 0, n}]/2^n;
%t A005650 a[n_] := A000681[n]*2^Floor[n/2]/n!;
%t A005650 Table[a[n], {n, 0, 19}]
%t A005650 (* _Jean-François Alcover_, Mar 14 2012, after _Shanzhen Gao_ *)
%K A005650 nonn,nice,easy
%O A005650 0,3
%A A005650 _N. J. A. Sloane_, _Simon Plouffe_
%E A005650 More terms from _Vladeta Jovovic_, Feb 11 2001