Given:
The given rule is

Domain of the function is the set of whole numbers greater than 0.
To find:
The first 4 terms of the sequence.
Solution:
We have,

Domain of the function is the set of whole numbers greater than 0. So, the domain for first four terms of the sequence are 1, 2, 3 and 4 respectively.
For n=1,



For n=2,



For n=3,



For n=4,



Therefore, the first 4 terms of the sequence are -6, 1, 20, 57 respectively.