How do you write an irrational number?

It is easier to answer the opposite: an irrational number cannot be written as:

• a ratio of two integers
• a terminating decimal
• a recurring decomal.

It can be written as an expression containing Irrational Numbers, such as 2*pi or 3*√2 or sin(37°) or log(3) or e2 or a combination of these or similar functions.