OFFSET
1,3
COMMENTS
We have the factorizations:
a(4) = 2^15 * 3^2 * 7^3.
a(5) = 2^59 * 3^15 * 5^9 * 7^5 * 11^6 * 23^5 * 29^4 * 41^4.
a(6) = 2^215 * 3^178 * 5^47 * 7^15 * 11^39 * 13^10 * 19^16 * 23^15 * 29^16 * 41^16 * 61^5 * 67^9 * 71^5 * 1931^16 * 3253^9.
LINKS
Richard Stanley, Table of n, a(n) for n = 1..6
Eric Weisstein's World of Mathematics, Bruhat Graph
Wikipedia, Permutohedron
EXAMPLE
For n=3 the permutohedron is a hexagon, which has six spanning trees.
PROG
(Python)
import sympy, itertools
def A337083(n):
p=tuple(itertools.permutations(range(n)))
m=len(p)
q={p[i]:i for i in range(m)}
Q=sympy.diag(*[n-1]*m)
for i in range(m):
for k in range(n-1):
Q[i, q[p[i][:k]+tuple(reversed(p[i][k:k+2]))+p[i][k+2:]]]=-1
return Q[:m-1, :m-1].det() # Pontus von Brömssen, Jan 18 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Richard Stanley, Aug 14 2020
EXTENSIONS
a(1) prepended by Pontus von Brömssen, Jan 19 2021
STATUS
approved