Let G$=\{0,1,\_\}$ be the tape alphabet for all TMs in this problem. Define the busy beaver function BB: N$->$N as follows: For each value of k$,$ consider all k$-$state TMs that halt when started with a blank tape. Let BB$($k$)$ be the maximum number of $1$s that remain on the tape among all of these machines. Show that BB is not a computable function.