The 40th number in the sequence will be 40 x 4, or 160.
Reasoning:
Because the sequence is multiples of 4.
The 1st number in the sequence is 1 x 4, or 4.
The 2nd number in the sequence is 2 x 4, or 8
...
The 4th number in the sequence is 4 x 4, or 16
...
The 17th number in the sequence is 17 x 4, or 68