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A259452
Number of 5 up, 5 down, 5 up, ... permutations of length 5n+1.
1
1, 1, 252, 578005, 6190034016, 214265281290061, 19157603395806362772, 3800502511986185228829385, 1498722661993096106927612109936, 1081056808393919319749313795137642521, 1336319624105519211256870506149168604698792
OFFSET
0,3
REFERENCES
P. R. Stein, personal communication.
LINKS
P. R. Stein & N. J. A. Sloane, Correspondence, 1975
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, 5*n+1, 0):
seq(a(n), n=0..10); # Alois P. Heinz, Jul 02 2015
MATHEMATICA
k = 5; b[u_, o_, t_] := b[u, o, t] = If[u + o == 0, 1, Sum[If[t == k, b[o - j, u + j - 1, 1], b[u + j - 1, o - j, t + 1]], {j, 1, o}]]; Array[b[0, k # + 1, 0] &, 10] (* Michael De Vlieger, Oct 15 2017, after Jean-François Alcover at A005983 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jun 28 2015
EXTENSIONS
More terms from Alois P. Heinz, Jul 02 2015
STATUS
approved