%I #9 Aug 16 2015 17:31:00
%S 1,1,1,20,228229620041151627,
%T 6559900643155884106407005800995037605507731066841784640626478359
%N Ceiling of ((2^n)!)/(4^n*2^(2*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]
%p f:=n->((2^n)!)/(4^n*2^(2*n^2));
%p [seq(ceil(f(n)),n=1..6)];
%Y Cf. A259326, A259327, A259328, A259329, A259330.
%K nonn
%O 1,4
%A _N. J. A. Sloane_, Jun 24 2015