Expanding an array....Interpolation?

Hello all,

I have a dataset like below:
3, 5, 6, 7, 4

I need to expand this dataset to 20 values. I would like to use a polynomial function to fit the curve.

In reality I will have 500 datasets of 35 to 45 points. I will need to expand them all to 100 equally spaced data points. Optimally I would retain the first and last values from the smaller dataset (35-45 dataset) and interpolate 98 points on the curve between those endpoints. Can I type one function and have that function output an array of those 100 new values off of that curve?

Thanks!!!