Hello SeqFans, Suppose that p,q,r,s are integers, and let a(n) be the number of triples (x,y,z) such that p*x + q*y + r*z = s, where x,y,z are all in {1,...,n}. It appears that (a(n)) is a linear recurrence sequence -- and that x,y,z can be replaced by x(1),x(2),...,x(k), etc. Can someone provide a reference? Thanks! Clark Kimberling