The expression "2i + 1" represents a mathematical formula where "i" is a variable. In this case, "2i" indicates that the variable is multiplied by 2, and then 1 is added to the result. This type of expression is often used in algebra to describe linear relationships or functions. In the context of mathematics, "2i + 1" can represent a sequence of numbers depending on the value of "i." For example, if "i" is 0, the expression equals 1; if "i" is 1, it equals 3. This illustrates how changing the variable affects the outcome of the expression.