A241591 Denominators of Postnikov's hook-length formula 2^n*(n+1)^(n-1)/n!.

1, 1, 1, 3, 3, 5, 45, 315, 35, 567, 14175, 1925, 467775, 868725, 7007, 638512875, 638512875, 14889875, 97692469875, 14849255421, 28868125, 17717861581875, 2143861251406875, 2505147019375, 236682282155319, 284473896821296875, 814172781296875, 3784415134680984375

Offset

0,4

References

Alexander Postnikov. Permutohedra, associahedra, and beyond. in: Conference in Honor of Richard Stanley's Sixtieth Birthday, June 2004. International Mathematics Research Notices, 6:1026-1106, 2009.

Links

Table of n, a(n) for n=0..27.

Matthew Wilson, Bruhat order on fixed-point-free involutions in the symmetric group, Electron. J. Combin., 21(2) (2014), #P2.20.

Example

1, 2, 6, 64/3, 250/3, 1728/5, 67228/45, 2097152/315, 1062882/35, 80000000/567, 9431790764/14175, 6115295232/1925, 7168641576148/467775, ...

Maple

t1:= [seq(2^n*(n+1)^(n-1)/n!, n=0..50)]:
t2:=map(numer, t1); # A241590
t3:=map(denom, t1); # A241591

Prog

(PARI) vector(30, n, n--; denominator(2^n*(n+1)^(n-1)/n!)) \\ Michel Marcus, Jul 18 2015

Crossrefs

Cf. A241590.

Has same start as A248592 but is a different sequence.

Sequence in context: A170919 A364661 A280779 * A248592 A132809 A265960

Adjacent sequences: A241588 A241589 A241590 * A241592 A241593 A241594

Keyword

nonn,frac

Author

N. J. A. Sloane, May 13 2014

Status

approved