Peter Flom already provided some links that should address your question but to state the answer directly: No, there is no table but a formula that make it possible to generate a series of apparently random numbers.
To get an idea of what is going on, you might consider some elementary pseudo-random number generators like the middle-square method or the linear congruential generator. The latter is deceptively simple and pretty common in general programming languages (probably not in serious statistical applications, though).
The details vary a little but these formulas (and others of the same kind) define a series of deterministic but apparently random values. As each number is generated using the previous one, the system simply saves the last number to pick the next one in the series. The seed, 123, is a way to reset this internal state to some known value to be able to reproduce a given series.