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%I #12 Jan 10 2017 11:06:15
%S 1,2,20,504,21032,1293418
%N Number of square permutations of 2n things.
%H Samuele Giraudo, S. Vialette, <a href="https://arxiv.org/abs/1601.05962">Unshuffling Permutations</a>, arXiv preprint arXiv:1601.05962 [cs.DS], 2016.
%e The 20 square permutations of order 4 are 1234, 1243, 1423, 1324, 1342, 4132, 3124, 3142, 3412, 4312, 2134, 2143, 2413, 4213, 2314, 2431, 4231, 3241, 3421, 4321.
%Y Cf. A191755 (square binary words).
%K nonn,more
%O 0,2
%A _N. J. A. Sloane_, Dec 15 2016
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