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A092491 a(n) = 2*A058094(n-2) - 5*A058094(n-3) + A058094(n-4) + a(n-1) for n >=4. 2
0, 0, 0, 0, 1, 6, 25, 93, 333, 1172, 4083, 14137, 48778, 167981, 577874, 1986747, 6828120, 23462470, 80611581, 276944893, 951422603, 3268470411, 11228209786, 38572124196, 132505812826, 455192771711, 1563706508759, 5371738013650 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

COMMENTS

A recurrence relation follows in a straightforward manner from the above formula and the recurrence relation for A058094.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..200

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

Index entries for linear recurrences with constant coefficients, signature (6,-11,9,-4,-4,1).

MAPLE

b[1]:=1:b[2]:=2:b[3]:=5:b[4]:=14:b[5]:=42:b[6]:=132: for n from 6 to 34 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:a[4]:=0: for n from 5 to 34 do a[n]:=2*b[n-2]-5*b[n-3]+b[n-4]+a[n-1] od: seq(a[n], n=1..34); # Emeric Deutsch, Apr 12 2005

MATHEMATICA

LinearRecurrence[{6, -11, 9, -4, -4, 1}, {0, 0, 0, 0, 1, 6}, 40] (* Vincenzo Librandi, Aug 15 2017 *)

CROSSREFS

Cf. A058094, A092489, A092490, A092492.

Sequence in context: A277973 A143815 A209241 * A112308 A034336 A291230

Adjacent sequences:  A092488 A092489 A092490 * A092492 A092493 A092494

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, Apr 04 2004

EXTENSIONS

Edited by Emeric Deutsch, Apr 12 2005

STATUS

approved

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Last modified July 15 16:09 EDT 2019. Contains 325049 sequences. (Running on oeis4.)