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A092489 Arises in enumeration of 321-hexagon-avoiding permutations. 6
0, 0, 1, 4, 14, 48, 165, 568, 1954, 6717, 23082, 79307, 272470, 936065, 3215741, 11047122, 37950140, 130369334, 447853808, 1538496047, 5285135093, 18155807539, 62369881206, 214256590058, 736026444181, 2528439830821 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,4
LINKS
Z. Stankova and J. West, Explicit enumeration of 321, hexagon-avoiding permutations, Discrete Math., 280 (2004), 165-189.
FORMULA
Stankova and West give an explicit recurrence.
a(n) = A058094(n) - A058094(n-1) for n >= 3. - Emeric Deutsch, May 04 2004
From Colin Barker, Aug 20 2019: (Start)
G.f.: x^3*(1 - 2*x + x^2 - x^3 - x^4) / (1 - 6*x + 11*x^2 - 9*x^3 + 4*x^4 + 4*x^5 - x^6).
a(n) = 6*a(n-1) - 11*a(n-2) + 9*a(n-3) - 4*a(n-4) - 4*a(n-5) + a(n-6) for n>7.
(End)
MAPLE
b[1]:=1: b[2]:=2: b[3]:=5: b[4]:=14: b[5]:=42: b[6]:=132: for n from 6 to 35 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: seq(b[n], n=1..35): a[1]:=0: a[2]:=0: for n from 3 to 35 do a[n]:=b[n]-2*b[n-1] od: seq(a[n], n=1..35); # here b[n]=A058094(n).
PROG
(PARI) concat([0, 0], Vec(x^3*(1 - 2*x + x^2 - x^3 - x^4) / (1 - 6*x + 11*x^2 - 9*x^3 + 4*x^4 + 4*x^5 - x^6) + O(x^30))) \\ Colin Barker, Aug 20 2019
CROSSREFS
Sequence in context: A289928 A007070 A204089 * A094827 A094667 A370051
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Apr 04 2004
EXTENSIONS
More terms from Emeric Deutsch, May 04 2004
STATUS
approved

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Last modified March 19 01:22 EDT 2024. Contains 370952 sequences. (Running on oeis4.)