Not So easy Maths

#1

I am unable to get any trick that should I use segmented sieve or any bit hacks is there.
And also what approach should be there for a counting problem.

#2

@02.adarsh.99
It is based on inclusion exclusion principle
lets say we had primes <= 6 = {2,3,5}
Ans = n/2 + n/3 + n/5 - n/6 - n/15 - n/10 + n/60

#3

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