A function is defined by f(0) = 0 and f(n) = f(n - 1) + 2n + 1 for n > 0. Find f(4).
f(1) = 0 + 2(1) + 1 = 3
f(2) = 3 + 2(2) + 1 = 8
f(3) = 8 + 2(3) + 1 = 15
f(4) = 15 + 2(4) + 1 = 24
