If it's no more than 5% of the features, it's actually n-choose-k(100,5) + n-choose-k(100,4) + n-choose-k(100,3) + n-choose-k(100,2) + 100!

    75,287,520
  +  3,921,225 
  +    161,700
  +      4,950
  +        100
  ------------
    79,375,495