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A229886 Number of 5 up, 5 down permutations of [n]. 2

%I

%S 1,1,1,1,1,1,1,6,21,56,126,252,2562,14442,59487,199627,578005,8330800,

%T 65056960,363823800,1628423880,6190034016,115452938151,1152005977431,

%U 8137667253101,45527993728141,214265281290061,4904624749585886,59578069604921361

%N Number of 5 up, 5 down permutations of [n].

%C Limit n->infinity (a(n)/n!)^(1/n) = 0.337596001995... . - _Vaclav Kotesovec_, Sep 06 2014

%H Alois P. Heinz, <a href="/A229886/b229886.txt">Table of n, a(n) for n = 0..545</a>

%e a(6) = 1: 123456.

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

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

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

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

%p end:

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

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

%Y Column k=5 of A229892.

%K nonn,eigen

%O 0,8

%A _Alois P. Heinz_, Oct 02 2013

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Last modified January 17 18:08 EST 2020. Contains 330987 sequences. (Running on oeis4.)