There are 456,456 possible three card spreads in a standard 78 card tarot deck. I love the symmetry of this number. As the spreads get bigger so does the number of possible combinations. But really as the spread is interpreted in all its subtleties the number is really nearly infinite. Each situation and question lends its own flavor to the reading.
Possible two card spreads- 6,006
After this the symmetry breaks down. There is something significant here.