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Search: id:A092490
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| 0, 0, 0, 1, 5, 20, 75, 271, 957, 3337, 11559, 39896, 137423, 472808, 1625632, 5587228, 19198971, 65963978, 226623902, 778551761, 2674604282, 9188106871, 31563807424, 108430368827, 372487292867, 1279591674070, 4395730089428
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OFFSET
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1,5
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COMMENT
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A recurrence relation follows in a straightforward manner from the above formula and the recurrence relation for A058094.
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REFERENCES
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Z. Stankova and J. West, Explicit enumeration of 321, hexagon-avoiding permutations, Discrete Math., 280 (2004), 165-189.
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FORMULA
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O.g.f.: -x^4*(1-x+x^2+x^3)/(-1+6*x-11*x^2+9*x^3-4*x^4-4*x^5+x^6). - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Dec 02 2007
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MAPLE
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b[1]:=1:b[2]:=2:b[3]:=5:b[4]:=14:b[5]:=42:b[6]:=132: for n from 6 to 32 do b[n+1]:=6*b[n]-11*b[n-1]+9*b[n-2]-4*b[n-3]-4*b[n-4]+b[n-5] od:a[1]:=0:a[2]:=0:a[3]:=0:for n from 4 to 32 do a[n]:=b[n]-3*b[n-1]+b[n-2] od: seq(a[n], n=1..32); (Deutsch)
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CROSSREFS
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Cf. A058094, A092489-A092492.
Cf. A058094.
Sequence in context: A094806 A026639 A022633 this_sequence A094828 A030191 A093131
Adjacent sequences: A092487 A092488 A092489 this_sequence A092491 A092492 A092493
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KEYWORD
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nonn,easy
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com), Apr 04 2004
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EXTENSIONS
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Edited by Emeric Deutsch (deutsch(AT)duke.poly.edu), Apr 12 2005
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