We find a recursion formula of the form:

, where  and 

and where p and q are constants:









(1)   









Divide through by 2



(2)   

Solve the system of equations (1) and (2)



Add the two equations:





substitute in (1)

(1)   
      
      

So the recursion formula is

 , where  and 

becomes

, where  and 

or

, where  and  

Substitute n=1 as a check









Substitute n=2 as a check









Substitute n=3:









Substitute n=4









So the sequence goes:

-1,2,12,40,112,288,704,1664,3840,8704,.......

Edwin