one method:

define the sequence as a function of , where is an integer.

so you have 5 points. (1,3), (2,4), (3,6), (4,8), and (5,12). now we want to find a curve that passes through all those points. let the curve be given by:

we have:

..............(1)

..............(2)

.............(3)

.........(4)

..........(5)

you have 5 equations, 5 unknowns. solve simultaneously