What does [ ] define in math?

Question

My teacher comes up with an expression saying:

an + (n+1)^{2} = 1/6[n(n + 1)(2n + 1) + 6(n + 1)^{2}]

I read on the internet that [ ] is used for a variaty of things. namingsly intervals, floor, etc. But in this situation what would they mean?

P.S an = n(n + 1)(2n + 1)/6

Answer 1

Compare $$\frac16(n(n+1)(2n+1)+6(n+1)^2)$$ with $$\frac16\left[n(n+1)(2n+1)+6(n+1)^2\right]$$

The expression is the same, but the readability and clarity is improved.

Answer 2

In the above context [] is the same as ()