how they got 11011100101 from 101?

they "Write the integers from 1 to 101 in binary notation successively from left to right"
i.e

1 10 11 100 101

thanks,understand :))
but i see that such given string will be very anormous when n is also big..
how this problem can be solved? i have no idea :( for such a big n_s :((