They are simply a set of numbers that have an unknown and unexplainable "power". The are somehow inexplicably linked to luck; good or bad, as Hurley finds out.
They are also the core values of the (fictional) Valenzetti Equation. A complex simulation used to calculate the amount of time before the end of the human race - the original reason that the Dharma Initiative came to the island. Dharma's mandate was to manipulate the forces of the island to somehow change these numbers, therefore changing the fate of humankind.