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%I #19 May 31 2021 16:58:56
%S 1,2,630,81729648000,256963707943060088053923840000000,
%T 30978254928194376001814792318154658399137088909801072314160618743948902400000000000000
%N a(n) = (2^n)!/4^n, with a(1)=1, a(2)=2.
%C The next term has 212 digits. - _Harvey P. Dale_, May 31 2021
%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]
%p a:= n-> ceil((2^n)!/4^n):
%p seq(a(n), n=1..6); # _Alois P. Heinz_, May 31 2021
%t Join[{1,2},Table[(2^n)!/4^n,{n,3,6}]] (* _Harvey P. Dale_, May 31 2021 *)
%K nonn,easy
%O 1,2
%A _N. J. A. Sloane_
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