%I #11 Mar 07 2020 07:48:43
%S 2,6,1120,36324288000,18272974787062050706056806400000,
%T 244766458691906180755079840538505942906762183978675139272380197483053056000000000000
%N a(n) = (2^n)!/(n!^2).
%H C. S. Lorens, <a href="http://dx.doi.org/10.1109/PGEC.1964.263724">Invertible Boolean functions</a>, IEEE Trans. Electron. Computers, EC-13 (1964), 529-541.
%H C. S. Lorens, <a href="/A000722/a000722.pdf">Invertible Boolean functions</a>, IEEE Trans. Electron. Computers, EC-13 (1964), 529-541. [Annotated scan of page 530 only]
%K nonn,easy
%O 1,1
%A _N. J. A. Sloane_