login
A321060
Number of ordered pairs (p,q) of permutations of [n] with equal up-down signatures and p(1)=q(1)=4.
2
10, 68, 852, 16328, 438496, 15608288, 707767328, 39729927744, 2700561836672, 218405906177792, 20715182759975936, 2276573425946788864, 286926691657095745024, 41104621803491951127552, 6641412815937114696669184, 1201977736831477123144658944
OFFSET
4,1
LINKS
MAPLE
b:= proc(u, o, h) option remember; `if`(u+o=0, 1,
add(add(b(u-j, o+j-1, h+i-1), i=1..u+o-h), j=1..u)+
add(add(b(u+j-1, o-j, h-i), i=1..h), j=1..o))
end:
a:= n-> (k-> b(k-1, n-k, n-k))(4):
seq(a(n), n=4..20);
CROSSREFS
Column k=4 of A262372.
Sequence in context: A081656 A219466 A330352 * A026958 A026988 A081280
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Oct 26 2018
STATUS
approved