The total number of functions, $$ f:\{1,2,3,4\} \rightarrow\{1,2,3,4,5,6\} $$ such that $f(1)+f(2)=f(3)$, is equal to :

Question

The total number of functions,

$$ f:\{1,2,3,4\} \rightarrow\{1,2,3,4,5,6\} $$ such that $f(1)+f(2)=f(3)$, is equal to :