Okay, so I'm somewhat slower than a speeding bullet....

If we maintain the same proportionate density, then to double the gravity means eight times the mass with twice the radius. Though the planet has 8 x more mass the distance to the core is doubled, and gravity obeys the inverse square law so the relative gravity is reduced by a factor of four. 8 / 4 gives us 2.

So far so good....

Following that same reasoning, a 35 G world with the same density as Earth would have 35 x the radius and 42,875 x the mass. Clearly, this cannot be so since this would give a planet well beyond the brown dwarf range and it would be a small red dwarf star. Hence, I adjusted my old figures based on the idea that a brown dwarf would be the max value for a planetary mass.

But we've specified a uranium core that suggests an overall density that's about 2.42 x greater than Earth's. (Uranium density = 19.1 g/cm^3 vs Iron density = 7.87 g/cm^3.) That reduces the mass by that 2.42 factor to 17,666 x Earth's.

The Earth's not solid iron, and has a density of 5.515 g/cm^2 according to Wiki, but I think you're assuming that the other stuff has the same density ratio as well.

To achieve that 35 G gravity with that mass we divide 17,666 by 35 and take the square root of that. That gives us a radius factor 22.46 x Earth's. That's nearly 0.21 x the Sun's radius.

So, a uranium core implies a mass of 17,666 x Earth's, or 0.053 x the Sun's mass, and a radius 0.21 x the Sun's.

Here's where I had a problem with this. Your mass calculation above was based on the premise that you were changing the mass but not the radius. If you now change the radius, the mass is going to change proportionally, and you don't have 35x Earth gravity any more.

Or something. Actually, I'm kinda scratching my head trying to figure out what you did here. So I'll just tell you how I would answer this, and maybe you can figure out where we disagree.

The gravitational attraction of a planet is proportional to (mass) / (radius) ^ 2. Since the mass goes like (density) x (radius) ^ 3, in terms of density and radius the gravitational attraction is proportional to (density) x (radius).

This is why, as any college physics teacher will tell you, it's better to do algebra and not put in actual numbers until the very end.

Anyway, you want an overall ratio of 35 for the gravitational attraction. The densities are in a ratio of 2.42. So you would need the radii in a ratio of 35 / 2.42 ~= 14.5. Krypton would need a radius of 14.5 Earths, or about 0.13 Suns.