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A005983
Number of 4 up, 4 down, 4 up, ... permutations of length 4n+1.
(Formerly M5347)
3
1, 1, 70, 26599, 33757360, 107709888805, 726401013530416, 9197888739246870571, 200656681438694771057920, 7065183006232334215872360169, 381446884048286939903298793116160, 30299510478473850351087119774475282895, 3422529682416045761005260546463028151218176
OFFSET
0,3
REFERENCES
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
P. R. Stein, personal communication.
LINKS
P. R. Stein and N. J. A. Sloane, Correspondence, 1975
MAPLE
b:= proc(u, o, t) option remember; `if`(u+o=0, 1, add(`if`(t=4,
b(o-j, u+j-1, 1), b(u+j-1, o-j, t+1)), j=1..o))
end:
a:= n-> b(0, 4*n+1, 0):
seq(a(n), n=0..20); # Alois P. Heinz, Oct 06 2013
MATHEMATICA
b[u_, o_, t_] := b[u, o, t] = If[u+o == 0, 1, Sum[If[t == 4, b[o-j, u+j-1, 1], b[u+j-1, o-j, t+1]], {j, 1, o}]] ; a[n_] := b[0, 4*n+1, 0]; Table[a[n], {n, 1, 20}] (* Jean-François Alcover, Nov 25 2014, after Alois P. Heinz *)
CROSSREFS
Cf. A229885.
Sequence in context: A145410 A177638 A274646 * A200313 A177642 A177644
KEYWORD
nonn
AUTHOR
EXTENSIONS
Typo in name fixed by Alois P. Heinz, Oct 06 2013
STATUS
approved