Email Print Irrational Number on 24 January 2016. Posted in Algebra An irrational number is a number that cannot be written as a fraction. \(\large{ \pi = 3.141592..... }\) \(\large{ \sqrt 2 = 1.414213... }\) \(\large{ \frac {19}{4} = 0.052632... }\) \(\large{ e=2.71828182... }\)