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A097119
Expansion of (1-x)^2/((1-x)^3-2x^4).
2
1, 1, 1, 1, 3, 9, 21, 41, 75, 141, 281, 577, 1179, 2369, 4709, 9353, 18659, 37365, 74889, 149937, 299827, 599289, 1198101, 2396137, 4793051, 9587421, 19175449, 38349409, 76695403, 153388273, 306778917, 613566153, 1227140787, 2454279365
OFFSET
0,5
FORMULA
G.f.: (1-2x+x^2)/(1-3x+3x^2-x^3-2x^4).
a(n) = 3a(n-1)-3a(n-2)+a(n-3)+2a(n-4).
a(n) = Sum_{k=0..floor(n/3)} binomial(n-k,3k)*2^k.
MATHEMATICA
CoefficientList[Series[(1-x)^2/((1-x)^3-2x^4), {x, 0, 50}], x] (* Harvey P. Dale, Feb 25 2011 *)
CROSSREFS
Sequence in context: A064999 A100135 A024173 * A374585 A146608 A161214
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Jul 25 2004
STATUS
approved