A196687 n!*A062868(n).

1, 4, 24, 336, 5520, 203040, 7025760, 510370560, 30163311360, 3577017024000, 319851801561600, 55850407258060800, 7021439018770176000, 1692163531361176473600, 284409062346887622144000, 90395009213694143422464000, 19571060809440210728706048000, 7929132907666579072319471616000

Offset

1,2

Comments

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

Links

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

Crossrefs

Cf. A062868, A196688.

Sequence in context: A206239 A374386 A361054 * A185457 A024250 A167140

Adjacent sequences: A196684 A196685 A196686 * A196688 A196689 A196690

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