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A099785 Sum C(n-k,3k)2^(n-3k), k=0..floor(n/4). 1
1, 2, 4, 8, 18, 48, 144, 448, 1380, 4152, 12224, 35456, 102024, 292768, 840416, 2416384, 6959504, 20069280, 57913536, 167158656, 482462752, 1392319488, 4017460224, 11590946816, 33439639616, 96470796672, 278311599616 (list; graph; refs; listen; history; internal format)
OFFSET

0,2

COMMENTS

In general a(n)=sum{k=0..floor(n/4), C(n-k,3k)u^k*v^(n-4k)} has g.f. (1-v*x)^2/((1-v*x)^3-u*x^4) and satisfies the recurrence a(n)==3v*a(n-1)-3v^2*a(n-2)+v^3*a(n-3)+u*a(n-4).

FORMULA

G.f.: (1-2x)^2/((1-2x)^3-2x^4); a(n)=6a(n-1)-12a(n-2)+8a(n-3)+2a(n-4).

CROSSREFS

Cf. A003522, A097119, A099786, A099787.

Sequence in context: A113989 A126757 A034766 * A166952 A135422 A116723

Adjacent sequences:  A099782 A099783 A099784 * A099786 A099787 A099788

KEYWORD

easy,nonn

AUTHOR

Paul Barry (pbarry(AT)wit.ie), Oct 26 2004

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Last modified February 14 22:12 EST 2012. Contains 205670 sequences.