4. [16] Given the sequence21 x1 x2 x3 x4 . . .

1 2 3 4 . . .

which of the two following explanations is preferable?

• x5 = 5, since ∀κ = 1, . . . , 4 : xκ = κ;

• x5 = 29, since xκ = κ4 − 10κ3 + 35κ2 − 49κ + 24.