We report on a comparative study of the transport properties of lightly La-
doped layered CaO (CaMnO3)(m) (m=1, 2, and infinity) and similar Mn3+/Mn4ratios. In contrast to the large and rather nonsystematic variations of the
resistivity rho(T) for samples with the same doping and various in, the ab
solute thermopower (S) exhibits remarkable systematics. In the paramagnetic
(PM) state, S varies linearly with temperature and its extrapolation to T=
0 has a finite intercept. The intercept and the slope of these lines vary s
ystematically with in. In particular, within the experimental error, the in
verse slopes of the straight lines increase linearly with 1/m, which in its
turn varies Linearly with the average number of Mn-Mn near neighbors. The
implications of this simple systematics are discussed using a model develop
ed by Cutler and Mott [Phys. Rev. 181, 1336 (1968)] for transport by activa
ted hopping of carriers obeying nondegenerate statistics. This model (or a
possible extension into the semidegenerate regime) leads also to a simple,
qualitative interpretation of S(T) of these materials on crossing the Neel
temperature (T-N) from the PM state and below T-N.