I think a better alternative could be to choose EVEN 5000 numbers (taking mod of 2 of any number out of these can help to check whether it can be in the set or not) and then make out set of 200 from these 5000 even numbers..
the set of 200 nos can be written on the disk in a sorted manner so that a binary search can be applied to them.. we can take out the first and the last number from the file and check whether its there or not.. and if its in range then apply binary search to find out the number.
