A196688 ((n!)^2-A196687(n))/2.

0, 0, 6, 120, 4440, 157680, 9187920, 557665920, 50759291520, 4795586208000, 636749560339200, 86796062772249600, 15877174512431232000, 2953945462595410483200, 712801595188655900928000, 173684063741850454560768000, 53471242848053479728254976000, 16530628080065352033845256192000

Offset

1,3

Comments

Let p = (p1..pn) and q = (q1..qn) be two random permutations of (1..n); call the pair (p,q) positive if the number of i with pi > qi is greater than the number of i with pi < qi. Then a(n) is the number of positive pairs.

Links

Table of n, a(n) for n=1..18.

Crossrefs

Cf. A062868, A196687. Equals n!*A179567(n).

Sequence in context: A029697 A248045 A280627 * A126448 A126446 A057003

Adjacent sequences: A196685 A196686 A196687 * A196689 A196690 A196691

Keyword

nonn

Author

Jan Lakota, Oct 04 2011

Extensions

a(1)-a(6) computed by Jan Lakota; extended by N. J. A. Sloane, Oct 04 2011

Status

approved