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A229886 Number of 5 up, 5 down permutations of [n]. 2
1, 1, 1, 1, 1, 1, 1, 6, 21, 56, 126, 252, 2562, 14442, 59487, 199627, 578005, 8330800, 65056960, 363823800, 1628423880, 6190034016, 115452938151, 1152005977431, 8137667253101, 45527993728141, 214265281290061, 4904624749585886, 59578069604921361 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,8

COMMENTS

Limit n->infinity (a(n)/n!)^(1/n) = 0.337596001995... . - Vaclav Kotesovec, Sep 06 2014

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..545

EXAMPLE

a(6) = 1: 123456.

a(7) = 6: 1234576, 1234675, 1235674, 1245673, 1345672, 2345671.

a(8) = 21: 12345876, 12346875, 12347865, 12356874, 12357864, 12367854, 12456873, 12457863, 12467853, 12567843, 13456872, 13457862, 13467852, 13567842, 14567832, 23456871, 23457861, 23467851, 23567841, 24567831, 34567821.

MAPLE

b:= proc(u, o, t) option remember; `if`(u+o=0, 1, add(`if`(t=5,

       b(o-j, u+j-1, 1), b(u+j-1, o-j, t+1)), j=1..o))

    end:

a:= n-> b(0, n, 0):

seq(a(n), n=0..35);

CROSSREFS

Column k=5 of A229892.

Sequence in context: A275936 A019500 A100356 * A243740 A137361 A058484

Adjacent sequences:  A229883 A229884 A229885 * A229887 A229888 A229889

KEYWORD

nonn,eigen

AUTHOR

Alois P. Heinz, Oct 02 2013

STATUS

approved

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Last modified December 8 14:38 EST 2019. Contains 329865 sequences. (Running on oeis4.)