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A092489 Arises in enumeration of 321-hexagon-avoiding permutations. 5
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

REFERENCES

Z. Stankova and J. West, Explicit enumeration of 321, hexagon-avoiding permutations, Discrete Math., 280 (2004), 165-189.

LINKS

Table of n, a(n) for n=1..26.

FORMULA

Stankova and West give an explicit recurrence.

a(n)=A058094(n)-A058094(n-1) for n >=3. - Emeric Deutsch, May 04 2004

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).

CROSSREFS

Cf. A058094, A092490-A092492.

Sequence in context: A289928 A007070 A204089 * A094827 A094667 A099376

Adjacent sequences:  A092486 A092487 A092488 * A092490 A092491 A092492

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 February 19 21:04 EST 2019. Contains 320328 sequences. (Running on oeis4.)