#include <cstdio>
#include <vector>
#define repeat(i, n) for (int i = 0; (i) < int(n); ++(i))
#define repeat_from(i, m, n) for (int i = (m); (i) < int(n); ++(i))
#define repeat_reverse(i, n) for (int i = (n)-1; (i) >= 0; --(i))
using ll = long long;
using namespace std;

constexpr int mod = 1e9+7;
int main() {
    int n, k; scanf("%d%d", &n, &k);
    const int dp_size = n * n + 3;
    vector<ll> cur(dp_size);
    cur[0] = 1;
    ll result = 0;
    repeat_reverse (i, n) {
        vector<ll> prv = move(cur);
        cur.assign(dp_size, 0);
        ll nxt = 1; repeat (j, i) nxt = nxt * (k + 1) % mod;
        repeat (a_i, min(k, i + 1) + 1) {
            repeat (delta, dp_size) if (prv[delta]) {
                result += (a_i + delta) % (i + 1) * nxt % mod * prv[delta] % mod;
                cur[delta + (a_i + delta) / (i + 1)] += prv[delta];
            }
        }
        repeat_from (a_i, (i + 1) + 1, k + 1) {
            repeat (delta, dp_size) if (prv[delta]) {
                result += (a_i + delta) * nxt % mod * prv[delta] % mod;
                cur[delta] += prv[delta];
            }
        }
        repeat (delta, dp_size) if (cur[delta]) {
            cur[delta] %= mod;
        }
        result %= mod;
    }
    printf("%lld\n", result);
    return 0;
}
