Quoccabank

Larissa the quokka works at a bank, and to pass the time will roll some standard six sided dice. She only knows one game, which is to roll six dice at once and hope to get all the numbers from one to six exactly once. She asks you what the probability of winning her game is.

Submit your answer as an irreducible fraction, with the numerator and denominator separated by a slash. For example, if your answer is $0.8$, you should submit "4/5".

For all the tasks, including this one, you can submit as many times as you like with no penalty! Only your best submission will be counted.