The sequence forms a group of factorials. Notice that 2! = 2 4! = 24 6! = 720 8! = 40320 10! = 3628800 Each number beside a factorial is an even number. The equation for even number is 2x. Therefore, the final equation is f(x) = 2x!
Verify x = 1, f(1) = 2(1)! = 2! x = 2, f(2) = 2(2)! = 4! x = 3, f(3) = 2(3)! = 6! and so on.
