[apache]

First off, yes, the 3520 was a typo, one I noticed and thought I fixed, but apparently did not.
Now, no no no, density has nothing to do with gravity. It is only distance and mass, and density is a function of mass and volume. At a distance of R from some mass M, the gravitational acceleration at that distance is constant, no matter how dense the mass is.
If you have a black hole with the mass of the sun, it will definitely be a few million times denser than the sun. However, the gravitational force on the earth from the black hole will be exactly the same as the force the sun has on the earth, if the earth orbited a black hole at the same distance it orbits the sun.
Now, if you were at the center of Jupiter, theoretically you would either experience infinite gravity or gravitational force based on the mass of the planet. Logic says its no gravity, but then again, there cannot be zero gravity, in fact there would at least have to be a force completely pulling you apart because you are completely surrounded by the mass of Jupiter.
But then again, we really do not know since we have never been to the center of any planet or moon or anything to see what the gravitational forces would be.