0, 3, 9, 18, 30, 45, 63,?

0, 3, 9, 18, 30, 45, 63, ? What number should replace the question mark?

This problem repeats another one in the library (at most with different numbers), so it's left out of browsing.

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #9233