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A000382
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Restricted permutations.
(Formerly M4087 N1696)
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3
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6, 11, 20, 36, 65, 119, 218, 400, 735, 1351, 2484, 4568, 8401, 15451, 28418, 52268, 96135, 176819, 325220, 598172, 1100209, 2023599, 3721978, 6845784
(list; graph; refs; listen; history; internal format)
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OFFSET
| 4,1
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REFERENCES
| N. S. Mendelsohn, Permutations with restricted displacement, Canad. Math. Bull., 4 (1961), 29-38.
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
| S. Plouffe, Approximations de S\'{e}ries G\'{e}n\'{e}ratrices et Quelques Conjectures, Dissertation, Universit\'{e} du Qu\'{e}bec \`{a} Montr\'{e}al, 1992.
S. Plouffe, 1031 Generating Functions and Conjectures, Universit\'{e} du Qu\'{e}bec \`{a} Montr\'{e}al, 1992.
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FORMULA
| a(n) = a(n-1)+a(n-2)+a(n-3)-2 (conjectured).
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MAPLE
| A000382:=-(-6+z+2*z**2+4*z**3+z**4)/(z-1)/(z**3+z**2+z-1); [Conjectured by S. Plouffe in his 1992 dissertation.]
a:= n-> if n<4 then 0 elif n=4 then 6 else (Matrix([[11, 7, 4, 2]]). Matrix(4, (i, j)-> if (i=j-1) then 1 elif j=1 then [2, 0, 0, -1][i] else 0 fi)^(n-2))[1, 4] fi: seq (a(n), n=4..27); [From Alois P. Heinz (heinz(AT)hs-heilbronn.de), Aug 26 2008]
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CROSSREFS
| Cf. A000496, A020992.
Sequence in context: A007745 A188556 A021011 * A192750 A000383 A205540
Adjacent sequences: A000379 A000380 A000381 * A000383 A000384 A000385
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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