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A001993
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Number of two-rowed partitions of length 3.
(Formerly M2452 N0973)
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9
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1, 1, 3, 5, 9, 13, 22, 30, 45, 61, 85, 111, 150, 190, 247, 309, 390, 478, 593, 715, 870, 1038, 1243, 1465, 1735, 2023, 2368, 2740, 3175, 3643, 4189, 4771, 5443, 6163, 6982, 7858, 8852, 9908, 11098, 12366, 13780, 15284, 16958, 18730, 20692, 22772, 25058, 27478
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OFFSET
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0,3
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REFERENCES
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G. E. Andrews, MacMahon's Partition Analysis II: Fundamental Theorems, Annals Combinatorics, 4 (2000), 327-338.
A. Cayley, Calculation of the minimum N.G.F. of the binary seventhic, Collected Mathematical Papers. Vols. 1-13, Cambridge Univ. Press, London, 1889-1897, Vol. 10, p. 408-419.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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Index entries for linear recurrences with constant coefficients, signature (1, 2, 0, -2, -4, 1, 3, 3, 1, -4, -2, 0, 2, 1, -1).
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FORMULA
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G.f.: 1/((1-x)*(1-x^2)^2*(1-x^3)^2*(1-x^4)).
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MAPLE
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a:= n-> (Matrix(15, (i, j)-> if (i=j-1) then 1 elif j=1 then [1, 2, 0, -2, -4, 1, 3, 3, 1, -4, -2, 0, 2, 1, -1][i] else 0 fi)^n)[1, 1]: seq(a(n), n=0..50); # Alois P. Heinz, Jul 31 2008
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MATHEMATICA
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a[n_] := (Table[Which[i == j-1, 1, j == 1, {1, 2, 0, -2, -4, 1, 3, 3, 1, -4, -2, 0, 2, 1, -1}[[i]], True, 0], {i, 1, 15}, {j, 1, 15}] // MatrixPower[#, n]&)[[1, 1]]; Table[a[n], {n, 0, 46}] (* Jean-François Alcover, Mar 17 2014, after Alois P. Heinz *)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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