IV’s is determinate between 0 and 31, so there is 32 possibilities for each stat.
32^6 = 1 073 741 824 combinations of different pokemon IV's.
Chance to get a 6*31 wild catch:
31 31 31 31 31 31
There is just one combination with theses IV’s, so the probability is 1 / 1 073 741 824.
The probability to catch a 6*0 wild pokemon is the same, 1 / 1 073 741 824.
Chance to get a 5*31 wild catch:
X 31 31 31 31 31
31 X 31 31 31 31
31 31 X 31 31 31
31 31 3