Question

What is formula ib this sequence 3 -16 12 -24 48?

Answer 1

Odd terms: `n_(i+1)=4n_i` where i is the number in the odd sequence from 1 and upwards
Even terms: `n_(i+1)= n_i-8` or `1 1/2 n_i`
Where i is the number in the even sequence from 1 and upwards

Explanation:

There might be multiple possibilities here, but one is at least that it is made up of two sequences.
1) 3, 12, 48: Next term is 4 times the current one.
2) -16 -24: Next term is either the current term -8 or the current term times 1 1/2. Without more terms, it is impossible to tell which is right.