Cn in terms of xn

Cn in terms of xn
                 
                 
-2 
-3 
-4 
-5 
-2  -6 
-7  14  -7 
-16  20  -8 
-30  27  -9 
Related problem: Express xn + 1/xn as a function of x + 1/x.

Reference: Abramowitz p. 797.