The asymmetric unit of the title compound, C(21)H(21)N(5)O(3), consists of two geometrically similar mol-ecules. The fused rings of the triazolo[4,5-d]pyrimidine system are nearly coplanar, making dihedral angels of 1.48 (18) and 1.34 (16)°, and the phenyl rings are twisted by 12.3 (1) and 8.7 (1)° with respect to the triazolopyrimidine plane. The ethyl groups of the n-butyl side chains are disordered over two sites in each of the independent mol-ecules, the ratios of occupancies being 0.60:0.40 and 0.61:0.39.