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Arguably, I would say that in this case 6 is the magic number ..
Stranding is based on the recognition that for circles of equal diameter, 6 will almost exactly fill the space around 1; next, one can see, that 12 fill the space around 6, 18 around 12, and so on ..
So, one needs to add 6 to the number in the outer ring each time to fill the next ring ..