Let A ={1,2,3,4,5} and B ={1,2,3,4,5,6}. Then the number of functions f: A → B satisfying f(1)+f(2)=f(4)-1 is equal to ____.

Let $\displaystyle \mathrm{A}=\{1,2,3,4,5\}$ and $\displaystyle \mathrm{B}=\{1,2,3,4,5,6\}$. Then the number of functions $\displaystyle f: \mathrm{A} \rightarrow \mathrm{B}$ satisfying $\displaystyle f(1)+f(2)=f(4)-1$ is equal to $\displaystyle \_\_\_\_$.