In the title compound, C(21)H(33)FN(3)O(2)P, the P atom has a distorted tetra-hedral environment and the N atoms display geometries consistent with a model of sp(2) hybridization (with bond-angle sums for the tertiary N atoms of 357.8 and 358.7°). The phosphoryl and carbonyl groups are anti with respect to each other. In the crystal, inversion dimers linked by pairs of N-H⋯O hydrogen bonds gene...

We investigate the long-term behavior of solutions of the difference equation[ x_{n+1}=x_{n}x_{n-3}-1 ,, n=0 ,, 1 ,, ldots ,, ]noindent where the initial conditions $x_{-3} ,, x_{-2} ,, x_{-1} ,, x_{0}$ are real numbers.  In particular, we look at the periodicity and asymptotic periodicity of solutions, as well as the existence of unbounded solutions.

In the title compound, C(18)H(17)N(5)O(2), the pyrimidine ring makes dihedral angles of 66.09 (12), 71.39 (13) and 56.7 (3)° with two phenyl rings and the nitro group, respectively. The dihedral angle between the two phenyl rings is 44.05 (14)°.

The title compound, C(15)H(22)BrN(3)O(2), consists of a pyridine ring with a bromine atom in the para position and two diethyl-amide groups in the ortho positions of the ring. Despite the positions of the three substituents on the pyridine ring, the mol-ecule does not exhibit either local or crystallographic twofold symmetry as the two diethyl-amido units exhibit significantly different N(py)-C...

In the title compound, C(18)H(19)N(5), the pyrimidine ring makes dihedral angles of 56.49 (9) and 70.88 (9)° with the phenyl rings. The dihedral angle between the two phenyl rings is 72.45 (9)°. No significant inter-molecular inter-actions are observed in the crystal structure.