OFFSET
0,2
COMMENTS
The sequence with g.f. 1/(1-r*x-r*x^2-r*x^3) has general term sum{k=0..n, T(n-k,k)r^(n-k)}.
LINKS
FORMULA
a(n)=sum{k=0..n, T(n-k, k)4^(n-k)}, T(n, k) = trinomial coefficients (A027907)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Feb 15 2005
STATUS
approved