0,2

In general a(n)=sum{k=0..floor(n/4), C(n-k,3k)u^k*v^(n-4k)} has g.f. (1-v*x)^2/((1-v*x)^3-u*x^4) and satisfies the recurrence a(n)==3v*a(n-1)-3v^2*a(n-2)+v^3*a(n-3)+u*a(n-4).

G.f.: (1-3x)^2/((1-3x)^3-x^4); a(n)=9a(n-1)-27a(n-2)+27a(n-3)+a(n-4).

Cf. A003522, A097119, A099785, A099787.

Sequence in context: A078226 A083591 A052917 this_sequence A131428 A099787 A146786

Adjacent sequences: A099783 A099784 A099785 this_sequence A099787 A099788 A099789

easy,nonn

Paul Barry (pbarry(AT)wit.ie), Oct 26 2004