Sqrt 13 and 1.1919919991... are irrational, meaning that they can't be described in a fraction of one integer over another, like 1/3, 45/44 or 57/107, these numbers are rational. Most irrationals are known constants like e or π, endless non-repeating decimals, or roots of non-perfect numbers like 13, 7, 5 or 2.
