In theory of indefinite sum, antidifference and finite calculus, the following difference functional equation and obtaining its some special solutions is very important $\bigtriangleup F(x):=F(x+1)-F(x)=f(x) \quad;\quad(1),$ where $\bigtriangleup$ is the forward difference operator and when $f$ is given and $F$ is unknown. Also, I know that if $D_f=\mathbb{R}$, then there exists a special solution $F_0(x)$ for equation (1) and we have the general solutions of it as follows $F=F_0+\lambda,$ which $\lambda$ is a one-periodic function. Now, in my research I deal to the following functional equation $F(x+1)+F(x)=f(x)$ , but I don't have any knowldge about it and its soloution. Any one can help me firstly, what does it call and secondly tell me some information about this. Thank you.