The second one is trickier.
Let's churn out the first few values and see how they relate to each other.
C_0 = 1
C_1 = 3
C_2 = 1
C_3 = 3
and so on.
These give differences of 2, -2, 2, -2... so we need a function of n that gives that. That can be done by using a variation of the original formula.
C_(n+1) = C_n - 2*(-1)^C_n