Calculation was invented well before writing.

Probably like a lot of other hunter gatherer groups, worked with 10 numbers at most- what they could count on their fingers.

I don't think they'd necessarily have a base-20 system built into the language if they didn't work with numbers larger than 10.

There's another set of countables on feet, for a total of 20.

Base-20 works well on one hand.

Using your thumb, start counting on the first bone in each finger. That gets you to four. Continue with the first joint (8), then the second bone (12), then the second joint (16) and finally the tips (20).

makes me think of how to count with the base 60 babylonian number system.

You'd use the thumb of one hand to count to 12 on the phalanges of the other 4 fingers, and keep track of every 5 passes like we would do with the second hand

5 fingers have 14 segments. Using segments on both sides of both hands = 2 sides of 2 hands = 56 finger segment slots. Counting the palms and backs of both hands = 4 hand sides = 60 segment slots and hand sides. Along with the 14 joints on 4 sides = 56 joint nodes = 116 joint nodes, segment slots and hand sides. Including the 10 finger (tips) gets a total of 126 and two arms is 128. Palms, backs of hands, arms, etc. could be further subdivided. Exercise: determine count of combinations.

And 32 with your fingers only, if you use each finger as a bit :)

31 really, because a fist is zero. Four also presents a minor difficulty.

If you use all 10, you can count up to 1024. :-)

I don't think Alaskans spend a lot of time looking at their toes. It's cold there.