A279200 Number of square permutations of 2n things.

1, 2, 20, 504, 21032, 1293418

Offset

0,2

Links

Table of n, a(n) for n=0..5.

Samuele Giraudo, S. Vialette, Unshuffling Permutations, arXiv preprint arXiv:1601.05962 [cs.DS], 2016.

Example

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.

Crossrefs

Cf. A191755 (square binary words).

Sequence in context: A012340 A279839 A279837 * A277414 A296789 A168136

Adjacent sequences: A279197 A279198 A279199 * A279201 A279202 A279203

Keyword

nonn,more

Author

N. J. A. Sloane, Dec 15 2016

Status

approved