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A262479 Number of ordered pairs (p,q) of permutations of [n] with equal up-down signatures and p(1)=q(1)=2. 2
1, 2, 8, 68, 952, 19312, 533544, 19209584, 873274112, 48904686848, 3307732742656, 265835173240320, 25041294346380800, 2732759857218994176, 342041866136488863232, 48672372916773453011968, 7813786873387535522529280, 1405550552561695118460387328 (list; graph; refs; listen; history; text; internal format)
OFFSET
2,2
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))(2):
seq(a(n), n=2..20);
CROSSREFS
Column k=2 of A262372.
Sequence in context: A093990 A361213 A156448 * A372315 A192550 A157752
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Sep 30 2015
STATUS
approved

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Last modified May 29 04:26 EDT 2024. Contains 372921 sequences. (Running on oeis4.)