Memoised function of C(n,k)

Write  a program in the form of top-down recursive function that used memoization to computer C(n,k) in the time complexity O(nk)

C(n,k) = C(n-1,k-1) + C(n-1,k)  if 0 < k < n
           =  1     if k = 0 or k = n
           =  0     otherwise

Do an experiment,  plot the number of call to C(n,k) in term of nk.  Compare this program with a version that does not use memoization.   Be careful not to overflow 32-bit integer.