Find formula for general term of 4, 9/2, 15/4, 20/8, ...

[Cobey]

The problem says:
Find the formula for the general term of the following sequence where n = 1 or greater:
4,9/2,15/4,20/8,...

Im not sure how to find the formula of the numerator, but the denominator should be 2^n-1 if n=1.
What is the formula for the numerator?

 

[stapel]

Find the formula for the general term of the following sequence where n = 1 or greater:

. . . . .$\displaystyle 4,\, \dfrac{9}{2},\, \dfrac{15}{4},\, \dfrac{20}{8},\,...$

Im not sure how to find the formula of the numerator, but the denominator should be 2^n-1 if n=1.
What is the formula for the numerator?

Even Wolfram Alpha can't figure out anything for this. Are you sure it's posted correctly?

 

[Deleted member 4993]

The problem says:
Find the formula for the general term of the following sequence where n = 1 or greater:
4,9/2,15/4,20/8,...

Im not sure how to find the formula of the numerator, but the denominator should be 2^(n-1) if n=1.
What is the formula for the numerator?

One of the functions that will fit the pattern would be:

Numerator = -1/3*n^3 + 2.5*n^2 - 1/6 * n + 2