Just a typo TLR, 4*4*4 != 64*4=256

! is the mathmatical symbol for "this number multiplied by every number lower than it, down to 1." For instance, 5! = 5*4*3*2*1.

The formula TLR used for figuring out how many flops give you the flush is the generic formula for choosing k things from a set of n things, where order of the things does not matter. So for the flush there's 11 cards of your suit left and you need to choose 3 of them to make a flop of that suit. Plug in for n and k and churn out the answer and that's the number of possible flops of your suit.