For any positive integers  $k_1,k_2$ and any set
$k_1,k_2$ and any set  $A\subseteq \mathbb {N}$, let
$A\subseteq \mathbb {N}$, let  $R_{k_1,k_2}(A,n)$ be the number of solutions of the equation
$R_{k_1,k_2}(A,n)$ be the number of solutions of the equation  $n=k_1a_1+k_2a_2$ with
$n=k_1a_1+k_2a_2$ with  $a_1,a_2\in A$. Let g be a fixed integer. We prove that if
$a_1,a_2\in A$. Let g be a fixed integer. We prove that if  $k_1$ and
$k_1$ and  $k_2$ are two integers with
$k_2$ are two integers with  $2\le k_1<k_2$ and
$2\le k_1<k_2$ and  $(k_1,k_2)=1$, then there does not exist any set
$(k_1,k_2)=1$, then there does not exist any set  $A\subseteq \mathbb {N}$ such that
$A\subseteq \mathbb {N}$ such that  $R_{k_1,k_2}(A,n)-R_{k_1,k_2}(\mathbb {N}\setminus A,n)=g$ for all sufficiently large integers n, and if
$R_{k_1,k_2}(A,n)-R_{k_1,k_2}(\mathbb {N}\setminus A,n)=g$ for all sufficiently large integers n, and if  $1=k_1<k_2$, then there exists a set A such that
$1=k_1<k_2$, then there exists a set A such that  $R_{k_1,k_2}(A,n)-R_{k_1,k_2}(\mathbb {N}\setminus A,n)=1$ for all positive integers n.
$R_{k_1,k_2}(A,n)-R_{k_1,k_2}(\mathbb {N}\setminus A,n)=1$ for all positive integers n.