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A006192
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Number of nonintersecting (or self-avoiding) rook paths joining opposite corners of 3 X n board.
(Formerly M3453)
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7
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1, 4, 12, 38, 125, 414, 1369, 4522, 14934, 49322, 162899, 538020, 1776961, 5868904, 19383672, 64019918, 211443425, 698350194, 2306494009, 7617832222, 25159990674, 83097804242, 274453403399, 906458014440
(list;
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OFFSET
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1,2
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REFERENCES
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H. L. Abbott and D. Hanson, A lattice path problem, Ars Combin., 6 (1978), 163-178.
S. R. Finch, Mathematical Constants, Cambridge, 2003, pp. 331-339.
Netnews group rec.puzzles, Frequently Asked Questions (FAQ) file. (Science Section).
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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D. G. Radcliffe, N. J. A. Sloane, C. Cole, J. Gillogly, & D. Dodson, Emails, 1994
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FORMULA
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a(n) = 4*a(n-1) - 3*a(n-2) + 2*a(n-3) + a(n-4) with a(0) = 0, a(1) = 1, a(2) = 4 and a(3) = 12. - Henry Bottomley, Sep 05 2001
G.f.: x*(1-x^2)/(1 - 4*x + 3*x^2 - 2*x^3 - x^4). - Emeric Deutsch, Dec 22 2004
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MATHEMATICA
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LinearRecurrence[{4, -3, 2, 1}, {1, 4, 12, 38}, 40] (* Harvey P. Dale, Oct 05 2011 *)
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PROG
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(Magma) I:=[1, 4, 12, 38]; [n le 4 select I[n] else 4*Self(n-1)-3*Self(n-2)+2*Self(n-3)+Self(n-4): n in [1..30]]; // Vincenzo Librandi, Oct 06 2011
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CROSSREFS
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KEYWORD
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nonn,walk,nice,easy
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AUTHOR
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STATUS
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approved
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