SemiPrimes := proc( n )
    local fact;
    fact := NumberTheory:-Divisors( n ) minus {1, n};
    if numelems( fact ) in {1,2} and not( member( 'false', isprime ~ ( fact ) ) ) then
        return n;
    else
        return NULL;
    end if;
end proc:
{ seq( SemiPrimes( i ), i = 1..100 ) };