780 is 30 (the number of letters in the string) multiplied by 26 (number of letters in the alphabet). I theorise that in the situation that there would be entirely "Z"s it would be 780/780
*edited to add: Alternately all "Z"s might be 0/780
*New edit: I've checked, it doesn't work I tested with the last string of numbers. Alternately it's possible that there's an alternate method of numeral assignment, but I've hit the end of my normal limit with this