(Garbage in, garbage out)
Level 1: 3
Level 2: -58.125
Level 3: -1.5
Level 4: 154.875
Level 5: 1650
What did you plug into that poor thing?
And what were you expecting instead?
What's the problem?
Not really.
It just depends on what you plug in as values.
Those from post #36 for example are not representable with a polynomial of degree 4.
As such, while you do get a formula, it's only ever a "nearly there".