No of blocks in database = 10000/5 = 2000
No of entries in 1st level index = No of blocks in memory
No of entries = 2000
20 entries per block
Total blocks = 2000/20 = 100
No of entries in 2nd level index = No of blocks at 1st level index
No of entries = 100
20 entries per block
Total blocks = 100/20 = 5
No of entries in 3rd level index = No of blocks at 2nd level index
No of entries = 5
20 entries per block
Total blocks = 5/20 = 1 (atleast one block)
Total no of blocks = 2000+100+5+1 = 2106