#include <bits/stdc++.h>
using namespace std;
const int CONST = 998244353;
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int n, k;
  cin >> n >> k;
  vector<int> A(n);
  for (int i = 0; i < n; i++) {
    cin >> A[i];
  }
  int ans = 0;
  sort(A.begin(), A.end());
  vector<vector<int> > dpcnt(n, vector<int>(k + 1));
  vector<vector<int> > prefcnt(n, vector<int>(k + 1));
  for (int x = 1; x * (k - 1) <= A[n - 1]; x++) {
    for (int i = 0; i < n; i++) {
      for (int j = 0; j <= k; j++) {
        prefcnt[i][j] = dpcnt[i][j] = 0;
      }
    }
    for (int i = 0; i < n; i++) {
      dpcnt[i][1] = 1;
      if (i != 0) {
        prefcnt[i][1] = prefcnt[i - 1][1];
      }
      prefcnt[i][1] += dpcnt[i][1];
    }
    int j = 0;
    for (int i = 0; i < n; i++) {
      while (j < i && A[i] - A[j] >= x) {
        j++;
      }
      j--;
      if (j != -1) {
        for (int d = 1; d < k; d++) {
          dpcnt[i][d + 1] += prefcnt[j][d];
          prefcnt[i][d + 1] = prefcnt[i - 1][d + 1] + dpcnt[i][d + 1];
          if (prefcnt[i][d + 1] >= CONST) {
            prefcnt[i][d + 1] -= CONST;
          }
          if (dpcnt[i][d + 1] >= CONST) {
            dpcnt[i][d + 1] -= CONST;
          }
        }
      } else {
        j++;
      }
    }
    for (int i = 0; i < n; i++) {
      ans += dpcnt[i][k];
      if (ans >= CONST) {
        ans -= CONST;
      }
    }
  }
  cout << ans;
  return 0;
}
