#ifdef LOCAL
#include "stdafx.h"
#else
#include <bits/stdc++.h>
#define IL inline
#define LL long long
#define eb emplace_back
#define sz(v) static_cast<int>((v).size())
#define L(i, j, k) for (int i = (j); i <= (k); ++i)
#define R(i, j, k) for (int i = (j); i >= (k); --i)
#define FIO(FILE) freopen(FILE".in", "r", stdin), freopen(FILE".out", "w", stdout)
using namespace std;

using vi = vector<int>;
#endif

constexpr int N = 2e3 + 9;
constexpr int P = 998244353;
int n, l[N];

IL int qpow (int b, int k = P - 2) {
  int r = 1;
  for (; k; k >>= 1, b = (LL)b * b % P) if (k & 1) r = (LL)r * b % P;
  return r;
}

int iv[N];

void init () {
  iv[1] = 1;
  L (i, 2, n) {
    iv[i] = (LL)iv[P % i] * (P - P / i) % P;
  }
}

IL int inv (int x) {
  return x <= n ? iv[x] : qpow(x);
}

int a[N], f[N], ns = 1;

void calc () {
  L (i, 1, n) {
    if (i > l[i]) {
      ns = 0;
    }
  }
  f[0] = 1;
  L (k, 1, n) {
    R (i, n, 0) {
      a[i] = min(l[i], n / 2);
      if (i + k <= n) {
        a[i] = min(a[i], a[i + k]);
      }
      if (i) {
        f[i] = a[i] < i ? 0 : (a[i] - i) / k + 1;
      }
    }
    int s = 1, x = 0;
    auto add = [&] (int t) {
      f[t] ? s = (LL)s * f[t] % P : ++x;
    };
    auto del = [&] (int t) {
      f[t] ? s = (LL)s * inv(f[t]) % P : --x;
    };
    L (i, 0, k - 1) {
      add(i);
    }
    if (!x && k <= a[0]) {
      ns = (ns + (LL)s * (a[0] / k)) % P;
    }
    L (p, 0, n / 2 - k + 1) {
      (ns += (x ? 0 : s)) %= P;
      del(p);
      add(p + k);
      if (l[p] < p) {
        break;
      }
    }
    if (k % 2 == 0) {
      s = 1;
      L (i, 0, k - 1) {
        int r = (i + k / 2) % k;
        a[i] < r ? s = 0 : s = (LL)s * ((a[i] - r) / k + 1) % P;
      }
      (ns += s) %= P;
    }
    R (i, n, 1) {
      a[i] = l[i];
      if (i + k <= n) {
        a[i] = min(a[i], a[i + k]);
      }
    }
    x = 0;
    L (i, 0, k - 1) {
      x += a[i] < i;
    }
    L (p, 0, n - k) {
      if (p + k - 1 > n / 2 && !x) {
        ++ns;
      }
      x += (a[p + k] < p + k) - (a[p] < p);
      if (l[p] < p) {
        break;
      }
    }
    ns %= P;
  }
}

int main () {
  ios::sync_with_stdio(0), cin.tie(0);
  cin >> n;
  init();
  L (i, 0, n) {
    cin >> l[i];
  }
  calc();
  cout << ns << '\n';
}
// I love WHQ!
// \\