Find the unit digit of the LCM of 73001–1 and 73001+1.
73001−1 and 73001+1 are consecutive even natural numbers
Hence, their HCF=2
LCM=product of numbers HCF=(78001)2−12=76002−12
76002 ends with 9 (use the concept of power cycle)
So 76002−1 ends in 8. We also know that as 76002 is a perfect square of an odd number, its tens digit will be even. So the required unit digit is 4.