i doubt whether i'm correct or not. please correct me if i'm wrong.
i tried drawing AVL trees with minimum nodes for height 2,3,4,5.
amd i observed that minimum no of internal nodes in an avl tree of height h I(h)=S(h-1)
minimum no of internal nodes in an avl tree of height 2 I(2)=S(1)=2
minimum no of internal nodes in an avl tree of height 3 I(3)=S(2)=4
minimum no of internal nodes in an avl tree of height 4 I(4)=S(3)=7
minimum no of internal nodes in an avl tree of height 5 I(5)=S(4)=12