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A169638
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Number of multiset permutations of the n initial elements of A005229 with additional element A005229(0)=1.
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2
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1, 1, 1, 4, 20, 60, 420, 3360, 30240, 151200, 1663200, 9979200, 129729600, 1816214400, 27243216000, 217945728000, 3705077376000, 66691392768000, 633568231296000, 12671364625920000, 266098657144320000, 5854170457175040000, 134645920515025920000, 1615751046180311040000
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OFFSET
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0,4
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LINKS
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FORMULA
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a(n) = number of permutations of the list b[0..n] where b(0)=0 and b(n) = A005229(n) for n>=1.
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MAPLE
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N:= 100: # to get a(0) to a(N)
procname(procname(n-2))+procname(n-procname(n-2))
end proc:
V:= Vector(N):
A[0]:= 1: V[1]:= 1:
for n from 1 to N do
V[r]:= V[r]+1;
A[n]:= A[n-1]*(n+1)/V[r];
od:
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MATHEMATICA
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Mallows[n_Integer?Positive] := Mallows[n] = Mallows[Mallows[n - 2]] + Mallows[ n - Mallows[n - 2]];
Mallows[0] = Mallows[1] = Mallows[2] = 1;
a[m_] := Length[Permutations[Table[Mallows[i], {i, 0, m}]]];
Table[a[m], {m, 0, 10}]
(* A much better way to compute the terms is to use the multinomials of the multiplicities of the terms of A005229! - Joerg Arndt, Dec 23 2014 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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