Built-in Mathematica Symbol

NumberQ

NumberQ[expr]
gives True if expr is a number, and False otherwise.

NumberQ[expr] returns False unless expr is manifestly a number (i.e., has head Complex, Integer, Rational or Real). » »

NumberQ tests whether an object is explicitly a number:

The expression must be manifestly a number:

You can test if a quantity represents a number with NumericQ:

On numerical coercion with N such quantities generally become numbers:

The same is true for complex and directed infinities:

They are both treated as Real:

Test if a matrix consists entirely of numbers:

Define a function that only evaluates when the argument is a number:

It does not evaluate with a symbolic argument:

It does evaluate when the argument is a number:

Use FindRoot to find all the solutions of the boundary value problem with

:

Plot the solutions:

NumberQ is equivalent to MatchQ[#, _Integer|_Rational|_Real|_Complex]&:

If NumberQ[x] is True, then NumericQ[x] is also True: