Numbers are drawn with your browser's cryptographic random generator, the same source used to create encryption keys, so every number in the range is equally likely and the results cannot be predicted.
With "No repeats" on, each number can appear only once, like drawing tickets from a hat. With it off, each draw is independent, like rolling a die.
Common questions
Are the numbers truly random?
They come from a cryptographically secure generator, which is unpredictable for all practical purposes, including prize draws.