Pi, the ratio of a circle’s circumference to its diameter, is known as an irrational number because it can’t be exactly expressed as a ratio of whole numbers. It would take an infinite number of digits to write it out in full as a decimal or, in binary form, as a string of 1s and 0s. The square root of 2, the square root of 3, and the constant e (the base of the natural logarithms) fall into the same category.
The known digits of these numbers appear patternless. According to one novel method of assessing the randomness of a sequence of numbers, however, the digits of pi turn out to be somewhat more irregular than the digits of the other irrational numbers.