If you did all of your arithmetic in hexadecimal, then C! would equal

C * B * A * 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1

Or 0x1C8CFC00


The decimal equivalents of C! and 0x1C8CFC00 are 12! and 479,001,600, respectively.