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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

4,1

LINKS

Alois P. Heinz, Table of n, a(n) for n = 4..110

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: A027242 A081656 A219466 * A026958 A026988 A081280

Adjacent sequences:  A321057 A321058 A321059 * A321061 A321062 A321063

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Oct 26 2018

STATUS

approved

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Last modified April 25 21:06 EDT 2019. Contains 322461 sequences. (Running on oeis4.)