Sequences and Series

Let R denote the set of all real numbers. Let f: R R be a function such that f(x) > 0 for all x R, and f(x + y) = f(x)f(y) for all x, y R. Let the real numbers a1, a2, , a50 be in an arithmetic progression. If f(a31) = 64f(a25), and i=150 f(ai) = 3(225 + 1), then the value of i=630 f(ai) is .