Which distributions have these Moment Generating functions?

M1(t)= (1/256) (1 + e^t) ^ 8

M2(t)= ( e ^ 2t) / [ ( 2 - e^t) ^ 2 ]

M3(t)= (4^ t^ 2) ( e^ 4t )

the numbers after M are subscripts. Does that mean they are 2nd and 3rd derivatives? I'm kinda lost. thank you for any help