  In this paper we define and study a vector-valued sequence space, called the
space of anisotropic $(s,q,r)$-summable sequences, that generalizes the
classical space of $(s; q)$-mixed sequences (or mixed $(s; q)$-summable
sequences). Furthermore, we define two classes of linear operators involving
this new space and one of them generalizes the class of $(s; q) $-mixed linear
operators due A. Pietsch. Some characterizations, inclusion results and a
Pietsch domination-type theorem are presented for these classes. It is worth
mentioning that some of these results are new even in the particular cases of
mixed summable sequences and mixed summing operators.
