A230382 Number of ascending runs of length n in the permutations of [2n].

1, 2, 21, 312, 5880, 133920, 3575880, 109549440, 3788104320, 145957593600, 6201593798400, 288084016281600, 14525808782284800, 790129980896256000, 46120599397192320000, 2875600728738017280000, 190740227037467627520000, 13411608375592258191360000

Offset

0,2

Links

Alois P. Heinz, Table of n, a(n) for n = 0..300

Formula

For n>0, a(n) = (n^2+n+1)*(2*n)!/((n+2)*n!). - Vaclav Kotesovec, Oct 18 2013

Maple

a:= proc(n) option remember; `if`(n<2, 1+n,
      2*(2*n-1)*(n+1)*(n^2+n+1)*a(n-1)/((n+2)*(n^2-n+1)))
    end:
seq(a(n), n=0..25);

Crossrefs

A diagonal of A122843.

Sequence in context: A094797 A359918 A234525 * A189489 A378099 A196629

Adjacent sequences: A230379 A230380 A230381 * A230383 A230384 A230385

Keyword

nonn

Author

Alois P. Heinz, Oct 17 2013

Status

approved