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A099579 Sum C(n-k,k-1)3^(k-1), k=0..floor(n/2). 1
0, 0, 1, 1, 7, 10, 40, 70, 217, 427, 1159, 2440, 6160, 13480, 32689, 73129, 173383, 392770, 919480, 2097790, 4875913, 11169283, 25856071, 59363920, 137109280, 315201040, 727060321, 1672663441, 3855438727, 8873429050, 20444528200 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,5

COMMENTS

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

LINKS

Table of n, a(n) for n=0..30.

Index entries for linear recurrences with constant coefficients, signature (1,6,-3,-9).

FORMULA

G.f.: x^2/((1-3x^2)(1-x-3x^2)); a(n)=a(n-1)+6a(n-2)-3a(n-3)-9a(n-4).

CROSSREFS

Cf. A097038, A099580.

Sequence in context: A241251 A126076 A258284 * A056521 A056510 A013398

Adjacent sequences:  A099576 A099577 A099578 * A099580 A099581 A099582

KEYWORD

easy,nonn

AUTHOR

Paul Barry, Oct 23 2004

STATUS

approved

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Last modified April 5 10:20 EDT 2020. Contains 333239 sequences. (Running on oeis4.)