<mathematics> A real number which is not a rational number, i.e. it is not the ratio of two integers.
The decimal expansion of an irrational is infinite but does not end in an infinite repeating sequence of digits.
Examples of irrational numbers are pi, e and the square root of two.
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Nearby terms: Ironman « ironmonger « IRQ « irrational number » irrefutable » IRSG » IRTF