I GIVE UP, seriouosly i've tried so many ways to figure this out but i just can't seem to see the pattern

Find the next two numbers in each sequence.

A) -1, 1 , 3 , 7 , 15 , ______ , _______

B) 3, 1, 2 , -1 , 3 , -4 , ______, _______

C) 16, 24, 36 , 54 , 81, ______, ______

just to show you I'm really trying hard, the next two terms for the second sequences are as follows (according to my calculations of course):

3, 1, 2 , -1 , 3 , -4 , 7, -11, 18