OFFSET
0,4
COMMENTS
In general a(n) = Sum_{k=0..floor(n/2)} C(n-k,k+2)*u^(n-k-2)*(v/u)^k has g.f. x^2/((1-u*x)^2(1-u*x-v*x^2)) and satisfies the recurrence a(n) = 3u*a(n-1)-(3u^2-v)*a(n-2)+(u^3-2uv)*a(n-3)+u^2^v*a(n-4).
LINKS
Index entries for linear recurrences with constant coefficients, signature (9,-23,3,36).
FORMULA
G.f.: x^2/((1-3*x)^2*(1-3*x-4*x^2)).
a(n) = 9*a(n-1)-23*a(n-2)+3*a(n-3)+36*a(n-4).
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Oct 25 2004
STATUS
approved