  The Landauer's formula conductance of the telescoped armchair nanotubes is
calculated with the Hamiltonian defined by first-principles calculations
(SIESTA code). Herein, partially extracting the inner tube from the outer tube
is called 'telescoping'. It shows a rapid oscillation superposed on a slow
oscillation as a function of discrete overlap length $(L-1/2)a$ with an integer
variable $L$ and the lattice constant $a$. Considering the interlayer
Hamiltonian as a perturbation, we obtain the approximate formula of the
amplitude of the slow oscillation as $|A|^2/(|A|^2+\varepsilon^2)$ where $A$ is
the effective interlayer interaction and $\varepsilon$ is the band split
without interlayer interaction. The approximate formula is related to the
Thouless number of the dispersion lines.
