  We study the homotopical minimal periods for maps on infra-solvmanifolds of
type (R) using the density of the homotopical minimal period set in the natural
numbers. This extends the result of [10] from flat manifolds to
infra-solvmanifolds of type (R). Applying our main result we will list all
possible maps on infra-solvmanifolds up to dimension three for which the
corresponding density is positive.
