For number of the form n=p, where p is prime, we have the function pi(x) for the number of such n<=x. And it is know that pi(x)=x/ln(x) approximately.

Is there a similar function for numbers which are the product of 2 primes? and a know approximation?

Any reference or link would help.

Thanks

https://mathworld.wolfram.com/Semiprime.html

An exact formula is given in the reference, but I was hoping for a simpler approximation formula.

Further references or links still welcome. Thanks.