Theorem. Let the column-vector of functions of,n T a(n):=, [a[0](n), a[1](n), a[2](n)] , be defined T by the initial conditions:, a(0) = [1, 0, 0] and a(n+1)=A(n)a(n), where A(n) is the, 3, by , 3, matrix 3 n 3 n (n + 1) 3 7 n + 4 3 n [[1/2, --- + 1/2, -----------], [- ---------, - ---------, - --- + 1/4], 4 8 2 (n + 1) 4 (n + 1) 8 3 3 n 5 n + 2 [----------, ----------, - ---------]] 2 2 8 (n + 1) 2 (n + 1) 4 (n + 1) T In other words, a(n)=A(n-1)A(n-2)...A(0) times, [1, 0, 0] Let 3 2 F(n, k) = binomial(n, k) (a[0](n) + a[1](n) k + a[2](n) k ) We have, for every non-negative integer n ----- \ ) F(n, k) = 1 / ----- k Proof: We cleverly construct / 3 3 3 | a[0](n) k a[1](n) k (6 n + 8 - 4 k) G(n, k) = binomial(n, k) |-1/2 ------------ + 1/8 -------------------------- | 3 3 \ (n + 1 - k) (n + 1 - k) 3 2 2 \ a[2](n) k (3 n - 3 n - 6 + 6 n k + 10 k - 4 k )| + 1/8 -------------------------------------------------| 3 | (n + 1 - k) / with the motive that F(n + 1, k) - F(n, k) = G(n, k + 1) - G(n, k) (check!) and the identity follows upon summing with respect to k. QED