carbon atoms or, when taken together with R13, represents a cyclic ring having 3-6 carbon atoms, or a residue represented by the following formula: ##STR3## (where R16 and R17 are each independently a hydrogen atom, a halogen atom, an alkyl group having 1-6 carbon atoms, an alkoxyl group having 1-6 carbon atoms or a cycloalkyl group; c is an integer of 1-3); a and b are each an integer of 1-3; d i