That sounds like the definition for Recursive Formula.
It is an expression.
A expression that only contains numbers is a Numerical
Constants (numbers), variables, the four basic operations of arithmetic (+, -, *, /) as well as brackets and indices (including negative and fractional ones).
It is evaluating the expression.
That type of sentence is called a mathematical expression.
An expression.
Expression
Algebraic expression
It is an expression.
Algebraic expressions is a mathematical phrase that contains operations numbers or variables.
They are terms of an expression or an equation
A expression that only contains numbers is a Numerical
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Constants (numbers), variables, the four basic operations of arithmetic (+, -, *, /) as well as brackets and indices (including negative and fractional ones).
An Algebraic Expression.
It is evaluating the expression.
An expression is made up of numbers and variables joined by mathematical operations.