Is this the division sign you mean: ÷ ?
( Image : google )
I typed Alt-246. Press and preserve the Alt key whilst you type 2 four 6 on the numeric keypad, no longer the numbers across the top of the keyboard. You need to have Num-lock on.
I use this most often to insert the degree symbol, that's Alt-248: °
Another beneficial one is Alt-241, that's the plus or minus symbol: ±
These are prolonged ASCII codes. They work on a PC. There is some thing similar on a Mac, however I don't know what it is. You should appearance it up at the internet.