  A novel theory of $F(R)$ gravity with the Lagrangian density ${\cal
L}=[R-(b/\beta)\arctan\left(\beta R\right)]/(2\kappa^2)$ is analyzed. Constant
curvature solutions of the model are found, and the potential of the scalar
field and the mass of a scalar degree of freedom in Einstein's frame are
derived. The cosmological parameters of the model are calculated, which are in
agreement with the PLANCK data. Critical points for the de Sitter phase and the
matter dominated epoch of autonomous equations are obtained and studied.
