Maths :P

f(x) = 2x
f'(x) = x^2
f''(x) = x^3 / 3
f'''(x) = x^4 / 12
f4(x) = x^5 / 60

f(2) = 4
f(3) = 9
f(4) = 21.33
f(5) = 52.0833
f(6) = 129.6

f^(n)(n+2) = 2x