In order to go from 1 to 10 you add a 0 to the end of the number. To go from 10 to 101 you add a 1 to the end of the number. In order to go from 101 to 1010 you again add a 0 to the end of the number. So it would appear that the pattern is to alternate between adding a 0 or 1 to the end of the number.
