OFFSET
0,2
COMMENTS
In general 1/(1-a*x-b*x^3) expands to sum{k=0..floor(n/3),C(n-2k,k)b^(n-2k)(a/b)^(n-3k)}.
LINKS
FORMULA
a(n)=2a(n-1)+3a(n-3); a(n)=sum{k=0..floor(n/3), binomial(n-2k, k)3^(n-2k)(2/3)^(n-3k)}.
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Oct 20 2004
STATUS
approved