You can calculate it roughly by using the so called Poisson-distribution (look in wikipedia). It is an easier version of the Gaussian distribution.
Anyway, the probability of getting AA is 1/220. If you calculate the probability of hitting 0,1,2,3,4... AA in 220 hands, it is the following:
0 times: 36.8%
1 time: 36.8%
2 times: 18.4%
3 times: 6.1%
4 time: 1.5%
5 times: 0.3%
6 times: 0.05%
So the probablity for hitting 6 AA in 180 hands is smaller than 0.05%.
Reagrds, MHFlush