Stuck here, please help

#1

Can you please tell me the logic for this problem.How to approach this

#2

For a given integer x,
you need to find the number of pairs <a,b> such that gcd(a,b)=1.
So, you need to find the number of pairs <a, x!/a> such that a ϵ {factors of x!}.

OR

It follows a pattern. I can give you a hint.
The task is to factor n! into a and b such that gcd(p,q)=1 and p<q. so we calculate the number of distinct primes in n!
Let prime factorisation of n!= (p1)^x1 * (p2)^x2 …(pk)^xk
now for each i, (pi)^xi can either go in p or q. hence 2^k ways. but as we want p<q. therefore only 2^(k-1) ways.

Hope, this would help.
Check this code if you implementation issues, https://ide.codingblocks.com/s/269499

#3

Nicely explained Devwrat, thnx a lot. Can u please tell me how to keep taking input from the user until he gives 0 as the input, 0 should not be taken as a input it’s just a sign to stop the proess.I have tried while(cin >> num), it’s not working

#4

Thanx again for the help

#5

Just do cin>>num, and inside the loop write a break statement.
if(num==0) break;

It will work.