Assume that none of the digits on the keypad are repeated. This means that we have 10 digits: 0,1,2,3,4,5,6,7,8,9.
The number of ways to arrange 10 distinct digits is
10! = 10*9*8*7*6*5*4*3*2*1 = 3,628,800
Answer: 3,628,800
That is 3 million, 628 thousand, and 800.
