How do you write the repeating symbol?

Answer 1

If we are thinking of decimals repeating to inifinity , then three 'dots/stops/periods are placed after the last number. e.g.

1 333... or 3.111... or 2. 545454....

The irrational number 'pi' is 3.1415926...

Answer 2

If a single digit is repeating then an ellipsis may be fine but that cab be ambiguous. For example, if you write 5/6 = 0.83... it is not clear whether you mean 0.838383... or 0.8333...

In manuscript it is easy to get around this: for a repeating string place a single dot over the first (or only) digit of the repeating string and another dot over the last digit. Thus 6/7 would be 0.857142 with a dot over the 8 and the 2. Unfortunately, many browser do not support these superscript dots and so I underline the repeating string and then add ... so that 6/7 appears as 0.857142... or better still, 0.857142... (repeating).