Sharp pental mode

[ijabbott]

(04-17-2018 02:16 PM)Dave Britten Wrote:  Sharp is the only place I've ever seen it, and I think I remember reading that it makes sense in the context of certain abacus designs.

Now that you mention it, I recall that Japanese abacuses (abaci?) are sort of base 5 + base 2 in that each decimal digit is split into 4 beads to count 0, 1, 2, 3, 4, plus another bead to count 0, 5.