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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 Alois P. Heinz, Table of n, a(n) for n = 2..150 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 Adjacent sequences: A262476 A262477 A262478 * A262480 A262481 A262482 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.)