1.递归（recursive）

fig01_02.

public class Recursive
{
    public static int f( int x )
    {
        if( x == 0 )
            return 0;
        else
            return 2 * f( x - 1 ) + x * x;
    }

    public static void main( String [ ] args )
    {

        System.out.println( "f(5) = " + f( 5 ) );
    }
}

结果：

f(5) = 141

fig01_03.