#include <bits/stdc++.h>
#pragma GCC diagnostic ignored "-Wunused-result"
#pragma GCC diagnostic ignored "-Wunused-function"
using namespace std;
namespace {
namespace shik {
template <class T>
void _R(T &x) {
  cin >> x;
}
void _R(int &x) { scanf("%d", &x); }
void _R(int64_t &x) { scanf("%" SCNd64, &x); }
void _R(double &x) { scanf("%lf", &x); }
void _R(char &x) { scanf(" %c", &x); }
void _R(char *x) { scanf("%s", x); }
void R() {}
template <class T, class... U>
void R(T &head, U &...tail) {
  _R(head);
  R(tail...);
}
template <class T>
void _W(const T &x) {
  cout << x;
}
void _W(const int &x) { printf("%d", x); }
void _W(const int64_t &x) { printf("%" PRId64, x); }
void _W(const double &x) { printf("%.16f", x); }
void _W(const char &x) { putchar(x); }
void _W(const char *x) { printf("%s", x); }
template <class T>
void _W(const vector<T> &x) {
  for (auto i = x.begin(); i != x.end(); _W(*i++))
    if (i != x.cbegin()) putchar(' ');
}
void W() {}
template <class T, class... U>
void W(const T &head, const U &...tail) {
  _W(head);
  putchar(sizeof...(tail) ? ' ' : '\n');
  W(tail...);
}
template <class T, class F = less<T>>
void sort_uniq(vector<T> &v, F f = F()) {
  sort(begin(v), end(v), f);
  v.resize(unique(begin(v), end(v)) - begin(v));
}
template <class T>
inline T bit(T x, int i) {
  return (x >> i) & 1;
}
template <class T>
inline bool chkmax(T &a, const T &b) {
  return b > a ? a = b, true : false;
}
template <class T>
inline bool chkmin(T &a, const T &b) {
  return b < a ? a = b, true : false;
}
template <class T>
using MaxHeap = priority_queue<T>;
template <class T>
using MinHeap = priority_queue<T, vector<T>, greater<T>>;
template <int _MOD>
struct ModInt {
  static const auto MOD = _MOD;
  template <class T>
  using integral_only = typename enable_if<is_integral<T>::value>::type;
  int x;
  constexpr ModInt() : x() {}
  template <class T, integral_only<T> * = nullptr>
  ModInt(T _x) {
    x = _x % MOD;
    if (x < 0) x += MOD;
  }
  ModInt operator-() const { return {x == 0 ? 0 : MOD - x}; }
  ModInt &operator+=(ModInt rhs) {
    x += rhs.x;
    if (x >= MOD) x -= MOD;
    return *this;
  }
  ModInt &operator-=(ModInt rhs) {
    x -= rhs.x;
    if (x < 0) x += MOD;
    return *this;
  }
  ModInt &operator*=(ModInt rhs) {
    x = (long long)x * rhs.x % MOD;
    return *this;
  }
  ModInt &operator/=(ModInt rhs) { return *this *= rhs.inv(); }
  ModInt operator+(ModInt rhs) const { return ModInt(*this) += rhs; }
  ModInt operator-(ModInt rhs) const { return ModInt(*this) -= rhs; }
  ModInt operator*(ModInt rhs) const { return ModInt(*this) *= rhs; }
  ModInt operator/(ModInt rhs) const { return ModInt(*this) /= rhs; }
  ModInt inv() const {
    int a = x, b = MOD, u = 1, v = 0;
    while (b != 0) {
      int t = a / b;
      a -= t * b;
      u -= t * v;
      swap(a, b);
      swap(u, v);
    }
    return u;
  }
  template <class T, integral_only<T> * = nullptr>
  ModInt pow(T e) {
    ModInt r = 1, p = *this;
    while (e) {
      if (e & 1) r *= p;
      p *= p;
      e >>= 1;
    }
    return r;
  }
  bool operator==(ModInt rhs) const { return x == rhs.x; }
  bool operator!=(ModInt rhs) const { return x != rhs.x; }
  bool operator<(ModInt rhs) const { return x < rhs.x; }
  bool operator<=(ModInt rhs) const { return x <= rhs.x; }
  bool operator>(ModInt rhs) const { return x > rhs.x; }
  bool operator>=(ModInt rhs) const { return x >= rhs.x; }
  friend string to_string(ModInt i) { return to_string(i.x); }
  friend ostream &operator<<(ostream &os, ModInt i) { return os << i.x; }
};
const int MOD = 1e9 + 7;
using mint = ModInt<MOD>;
const int K = 2010;
int n, m;
mint _dp[2][K];
auto dp = _dp[0], dq = _dp[1];
void main() {
  R(n, m);
  dp[0] = 1;
  for (int i = n; i >= 1; i--) {
    for (int k = 0; k < int(K); k++) dq[k] = 0;
    int u = min(i, m);
    for (int j = (0); j <= int(u); j++) {
      for (int k = 0; k < int(K); k++)
        if (dp[k].x != 0) {
          dq[(j + k) / i + k] += dp[k];
        }
    }
    if (m > i) {
      for (int k = 0; k < int(K); k++) dq[k] += dp[k] * (m - i);
    }
    swap(dp, dq);
  };
  mint s = 0;
  for (int i = 0; i < int(K); i++) s += dp[i] * i;
  ;
  mint ans = 1;
  ans *= n;
  ans *= m * (m + 1) / 2;
  for (int i = 0; i < int(n - 1); i++) ans *= m + 1;
  ;
  ans -= s;
  W(ans);
}
}  // namespace shik
}  // namespace
int main() {
  shik::main();
  return 0;
}
