\\ Number of maximal product-free subsets of {1..n}.
\\ Main recursive function has the following arguments:
\\    k: Indicates elements from 2..k have been picked.
\\    b: bitmap of chosen elements.
\\ Optimisation: Elements over n\2 can be freely added once k reaches half their value if
\\ permitted by the current selection. In fact, for the set to be maximal they must be added.
A326496(n)={
    my(lim=vector(n, k, sqrtint(k)));
    my(accept(b,k) = for(i=2, lim[k], if(bittest(b,i) && !(k%i) && bittest(b,k/i), return(0))); 1);
    my(ismaxl(b)=
      for(k=2, n\2, if(!bittest(b,k) && accept(b,k),
        my(f=0);
        for(i=2, n\k, if((i==k || bittest(b,i)) && bittest(b,k*i), f=1; break));
        if(!f, return(0));
       ));
      1
    );
    my(recurse(k, b)=
      for(j=max(2*k,n\2+1), min(2*k+1,n), if(accept(b,j), b += (1<<j)));
      k++;
      if(k > n\2, ismaxl(b), self()(k, b) + if(accept(b,k), self()(k, b + (1<<k))));
   );
   recurse(1, 0);
}

\\ End