OFFSET
0,5
LINKS
Index entries for linear recurrences with constant coefficients, signature (3,-3,1,2).
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
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Jul 25 2004
STATUS
approved