WarriorofToys is almost certainly correct. When it comes to numbers, most people's brains have trouble coping with strings of more than four or five. For 27 years I worked in computing and found that remembering strings of three numbers was easy and I can still remember lots of them, even where the same number was used for different purposes, e.g. centre (school) 103 was Bedale School and subject 103 was Art and Design, and we would use the codes in conversation or internal notes instead of the actual centre name or subject name, such as "Can you replace entries for 125 for centre 027 with subject 126". Later on, subject numbers became four characters, some with an alphabetical character added at the end and centre numbers became 5 digit ones and the effect was pretty well immediate, you referred to a computer printout to check what the number stood for! With time, you remembered the codes of the subjects you were responsible for and the numbers of the centres which were particularly good or troublesome, but that was all.
It's the same with 'phone numbers, people group them into strings, generally of no more than five numbers.
