6: The sequence goes
a₁ = 3/5,
a₂ = 1/5,
a₃ = −1,
a₄ = −3.

When n tends to infinity, the terms n² in both the denominator and the numerator prevail (see intuitive calculation) and the sequence is about n²/n² = 1.

Next hint - boundedness
Next hint - monotonicity
Answer