P-adic number
In number theory, given a prime number p, the p-adic numbers form an extension of the rational numbers that is distinct from the real numbers, though with some similar properties; p-adic numbers can be written in a form similar to (possibly infinite) decimals, but with digits based on a prime number p rather than ten, and extending to the left rather than to the right. For example, comparing the expansion of the rational number 1 5 {\displaystyle {\tfrac {1}{5}}} in base 3 vs.