How do you show a reccuring number in maths?

A recurring, or repeating, decimal in math is usually expressed by either placing a line over the repeating numbers, or by adding an ellipsis (three periods, "...") after the repeating numbers.

For example: 2/3 can be represented as 0.666..., and 27/7 can be represented as 3.857142857142... You could have also placed a line over the "666" and the "857142" in those examples.