jMol series arm-chair nanotube

Here's a single-walled (5,5) carbon nanotube with arm-chair (as opposed to zig-zag) chirality. Its size and structure is chosen so that it can be seamlessly capped by half of a buckyball. Suppose we wanted to sheath a facing pair of these capped tubes in a larger nanotube, so that the carbon atoms of the outer tube were approximately 3.4 Angstroms (graphite's normal inter-layer spacing) away from the inner tube atoms. Given that this tube has 5 "armchairs" like this => running around its circumference, how many "armchairs of circumference" should the outer tube have?

When that 2-wall internally-capped tube model is constructed, we'll compare it to the image below of a 15-wall nanotube with a 6-wall internal closure:

The above image is tiny part of a much larger image of multi-walled carbon nanotubes lying like straight sticks of uncooked spaghetti after falling out of the box into a pot on the stove.

For more nano-tube and nano-cone models, check out Steffen Weber's jnanotube applet.
Hop to model number four here.