A013498 Number of permutations in S_n with a certain property.

1, 0, 1, 3, 5, 12, 22, 50, 95, 210, 406, 882, 1722, 3696, 7260, 15444, 30459, 64350, 127270, 267410, 529958, 1108536, 2200276, 4585308, 9111830, 18929092, 37650172, 78004500, 155266100, 320932800, 639191160

Offset

1,4

Links

Table of n, a(n) for n=1..31.

Frank Schmidt and Rodica Simion, Card shuffling and a transformation on S_n, Aequationes Math. 44 (1992), no. 1, 11-34.

Maple

binomial(n-2, floor(n/2)-1) + floor((n-1)/2)*binomial(n-3, floor(n/2)-2);

Crossrefs

Sequence in context: A191391 A121482 A368858 * A161624 A247794 A034758

Adjacent sequences: A013495 A013496 A013497 * A013499 A013500 A013501

Keyword

nonn,easy

Author

N. J. A. Sloane.

Status

approved