How many humans are needed in order to sustain and grow a steady population in a habitable area? Assume resources are adequate and the environment is favorable.

To further refine this question, let's assume this is an early spacefaring technology scenario, such as putting a colony on a neighboring planet (same system) with earth-like conditions with a technology level either current or near-future. Assume the population has a mix of professions suitable for the new environment (resource gatherers, physicians, etc.).