each element has 2 states, there or not there, so there are
2^100 different ways of choosing sets there or not there, including none of them there (the empty set)
so there are
2^100 - 1 non empty subsets
100C1 + 100C2 have 2 or less elements
2^100 - 1(0 element) - 100C1(1 element) - 100C2(2 element) = 2^100 - 1 - 100 - 4950 = 2^100 - 5051
more than 2= tatal-(less than 2 include 2)
