#include <iostream>
#include <vector>
using namespace std;

int main(){
    int N, K;
    cin >> N >> K;
    long array_patterns[N + 1][N * (N + 1) / 2 + 1]; // now_array_size, now_inversion_number
    for(int i = 0; i <= N * (N + 1) / 2; i++){
        array_patterns[N][i] = (i <= K);
    }
    vector<long> array_patterns_cumulative_sum[N + 1];
    array_patterns_cumulative_sum[N].push_back(0);
    long cumulative_sum_last = 0;
    for(int i = 0; i <= N * (N + 1) / 2; i++){
        cumulative_sum_last += array_patterns[N][i];
        array_patterns_cumulative_sum[N].push_back(cumulative_sum_last);
    }
    for(int i = N - 1; i >= 0; i--){
        for(int j = 0; j <= i * (i + 1) / 2; j++){
            array_patterns[i][j] = (array_patterns_cumulative_sum[i + 1][i + j + 1] - array_patterns_cumulative_sum[i + 1][j]) % long(1e9 + 7);
        }
        array_patterns_cumulative_sum[i].push_back(0);
        long cumulative_sum = 0;
        for(int j = 0; j <= i * (i + 1) / 2; j++){
            cumulative_sum += array_patterns[i][j];
            array_patterns_cumulative_sum[i].push_back(cumulative_sum);
        }
    }
    cout << array_patterns[0][0] << endl;
}