We present the group-theoretic structure of the classes of multiplicative and firmly multiplicative arithmetical functions of several variables under the Dirichlet convolution, and we give characterizations of these two classes in terms of a derivation of arithmetical functions.
MSC: 11A25f (n 1 ) · · · f (n r ) is firmly multiplicative. On the other hand, the function gcd(n 1 , . . . , n r ) is multiplicative but not firmly multiplicative for r ≥ 2. Further examples can be found, e.g., in [5,10,11]. A survey on multiplicative arithmetical functions of several variables is presented in [11].An arithmetical function f ∈ A r (R) is said to be additive if f (m 1 n 1 , . . . , m r n r ) = f (m 1 , . . . , m r ) + f (n 1 , . . . , n r ) for all positive integers m 1 , . . . , m r and n 1 , . . . , n r with (m 1 · · · m r , n 1 · · · n r ) = 1, and an arithmetical function f ∈ A r (R) is said to be completely additive if f (m 1 n 1 , . . . , m r n r ) = f (m 1 , . . . , m r ) + f (n 1 , . . . , n r )