  Ferromagnetiam and superconductivity in a two-dimensional triangular-lattice
Hubbard model are studied using the density-matrix renormalization group
method. We propose a mechanism of the {\it f}-wave spin-triplet pairing derived
from the three-site cyclic-exchange ferromagnetic interactions. We point out
that a triangular network of hopping integrals, which is required for the
three-site cyclic hopping processes, is contained in the (possibly)
spin-triplet superconducting systems, such as Bechgaard salts (TMTSF)$_2$X,
cobalt oxide Na$_{0.35}$CoO$_2$$\cdot$1.3H$_2$O, and layered perovskite
Sr$_2$RuO$_4$.
