That's not quite right. Remember that grouped numbers count as a singular number within some limits. For example, if I was trying to remember a phone number in my working set: 1-2-3 4-5-6 7-8-9-0 that would be too large, but if I group the numbers: 12-3 45-6 78-90 then now it fits. Of course, most adults will remember that number like this: 123 456 78-90

When you're multiplying large numbers you only need around 5 or 6 items.