What's the easiest way to see if a sphere intersects with another using insideUnitSphere

Hello, I am trying to create multiple clusters of objects in a sphere radius, however these clusters should not intersect with one another. Here is a visual of how it should be: ![alt text][1] [1]: /storage/temp/133380-example.png So I have this to get my radius: public Vector3 GetCircleRadius(Vector3 center, float maxDistance) { return (Random.insideUnitSphere + center) * maxDistance; } Say I would call that method twice on a different center & max distance. What would be the easiest formula I can use to check if these 2 Vector3's overlap eachother? Thanks for any suggestions! Kr, Shady