函數等式

Question

給定函數fun，Rec的數學公式是什麼？

public class Fun { 

    public static int Rec(int n) { 

    if ((n==1) || (n==2)) 
     return 1; 
    else { 
     int result = 0; 
     for(int i=2; i<=(n-1); i++) 
     result = result+Rec(n-1)+ Rec(n-2); 

     return result; 
    } 
    } 
} 

Answer 1

f(0) = 0 
f(1) = 1 
f(2) = 1 
f(3) = 2 
f(4) = 6 
f(5) = 24 
f(6) = 120 
f(7) = 720 
f(8) = 5040 
f(9) = 40320 
f(10) = 362880 
f(11) = 3628800 

樣子（N-1）！