I have absolutely no idea where to start.
There are 9 1-digit numbers, 90 2-digit numbers, 900 3-digit numbers and 9000 4-digit numbers. Hence the last digit of the last 4-digit number is in position
The last digit of the last 5-digit number will be in position which is greater than 206787. Hence the number we are looking for is a 5-digit number. The position of the last digit of the 5-digit number is Now find the largest such that
So that number is whose last digit is in position 206784. The next 5-digit number is 43579 and the 206787th digit in the sequence is the 3rd digit of this number, which is 5.