Strictly speaking, you should use round brackets

( ) for this. But, in order to distinguish comments from algebra, we always use round brackets for comments and employ a combination of round

( ), square

[ ] and curly

{ } brackets for formulae - depending upon what seems clearest at the time.

Again, strictly speaking, expressions such as Y=Σ(X) are used by mathematicians to indicate Y is some 'function' of X - in this case Y is the sum of X, and X is a list of items. This arrangement applies to other functions, such as logarithms - as in Y=log(X), where X and Y may be either single values, or sets of numbers.