When you roll a pair of dice there are 6 x 6= 36 possible combinations. To get a "7" you must roll (6, 1), (5, 2), (4, 3), (3, 4), (2, 5), or (1, 6). So the probability of getting a "7" is 6/36= 1/6. To get an "11" you must roll (6, 5) or (5, 6). So the probability of getting "11" is 2/36= 1/18. The probability of getting either a "7" or an "11" is 1/6+ 1/18= 3/18+ 1/18= 4/18= 2/9. The probability of doing that 17 times in a row is \(\displaystyle (2/9)^{17}\). That is approximately 0.000000000000786.