I can't figure out this problem. Any help is appreciated.

Suppose h0, h1, h2,..... is a sequence defined as follows:

h0 = 1, h1 = 2, h2 = 3

hk = hk-1 + hk-2 + hk-3 for all ints k is greater than or equal to 3.

Prove that hn is less than or equal to 3^(n).

Thank you!