#include<iostream>
#include<algorithm>
#include<cstring>

using namespace std; 

const int N = 1e3 + 5, mol = 998244353, M  = 2e4;

int n;
int q[N];
int dp[N][2*M+5], ans;

signed main()
{
    ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    
    cin >> n;
    
    for(int i = 1; i <= n ; i ++) cin >> q[i];
    
    for(int i = 1; i <= n ; i ++)
    {
        ans ++;
        for(int j = 1; j < i ; j ++)
        {
            dp[i][q[i] - q[j] + M] += dp[j][q[i]-q[j] + M] + 1;
            dp[i][q[i] - q[j] + M] %= mol;
            ans += dp[j][q[i]-q[j] + M] + 1;
            ans %= mol;
        }
    }
    
    cout << ans << endl;
    
    return 0;
}

我比较疑惑的是为什么用dp[j][q[i]-q[j] + M] + 1作为对ans的贡献,而不是用dp[i][q[i] - q[j] + M]