| 1 | So there's no N factorial involved here. | |
| 2 | Divided by NA factorial times the same thing for B. | |
| 3 | Like particles, you have to divide by N factorial. . | |
| 4 | Write a function that calculates a number's factorial using recursion. | |
| 5 | That is, now we have to divide by NA factorial times NB factorial. |