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a(n) = (2^n)!/(n!^2).
3

%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_