How many numbers of at least three digits can be formed from the indegers 1,2,3,4,5,6

The answer is 1920, right? Here is how-

The numbers must contain at least three digit and can go above that which means the answer has 3 4 5 and 6 digits all together.

For three digits, there will be 6*5*4 = 120

For 4 Digits, There will be 6*5*4*3=360 possible numbers

For 5 digits, there will be 6*5*4*3*2 = 6! = 720

For 6 digits, there will be 6*5*4*3*2*1 = 6! = 720

Now add them up = 120+360+2*720 = 1920