btw, that number she has on the blackboard can be represented by something like 66 bits.

18 446 744 073 709 551 615 is the largest number representable by an unsigned 64 bit integer

256 bits:

115 792 089 237 316 195 423 570 985 008 687 907 853 269 984 665 640 564 039 457 584 007 913 129 639 936

that's 78 digits (26*3)