#include<bits/stdc++.h>
using namespace std;
namespace my_std{
	#define ll long long
	#define bl bool
	ll my_pow(ll a,ll b,ll mod){
		ll res=1;
		if(!b) return 1;
		while(b){
			if(b&1) res=(res*a)%mod;
			a=(a*a)%mod;
			b>>=1;
		}
		return res;
	}
	ll qpow(ll a,ll b){
		ll res=1;
		if(!b) return 1;
		while(b){
			if(b&1) res*=a;
			a*=a;
			b>>=1;
		}
		return res;
	}
	#define db double
	#define pf printf
	#define pc putchar
	#define fr(i,x,y) for(register ll i=(x);i<=(y);i++)
	#define pfr(i,x,y) for(register ll i=(x);i>=(y);i--)
	#define go(u) for(ll i=head[u];i;i=e[i].nxt)
	#define enter pc('\n')
	#define space pc(' ')
	#define fir first
	#define sec second
	#define MP make_pair
	#define il inline
	#define inf 8e18
	#define random(x) rand()*rand()%(x)
	#define inv(a,mod) my_pow((a),(mod-2),(mod))
	il ll read(){
		ll sum=0,f=1;
		char ch=0;
		while(!isdigit(ch)){
			if(ch=='-') f=-1;
			ch=getchar();
		}
		while(isdigit(ch)){
			sum=sum*10+(ch^48);
			ch=getchar();
		}
		return sum*f;
	}
	il void write(ll x){
		if(x<0){
			x=-x;
			pc('-');
		}
		if(x>9) write(x/10);
		pc(x%10+'0');
	}
	il void writeln(ll x){
		write(x);
		enter;
	}
	il void writesp(ll x){
		write(x);
		space;
	}
}
using namespace my_std;
#define mod 998244353
ll n,lim[2020],nxt[2020][2020],a[2020],invv[2020],ans=0;
il ll solve2(ll x,ll len){
	fr(i,0,len-1) if(nxt[i][len]<(x+i)%len) return 0;
	if((len-1)>=(n+1)/2){
		ll maxx=0;
		fr(i,0,n){
			maxx=max(maxx,(x+i)%len);
			if((maxx+(x+n-i)%len)>n) return 0;
		}
		return 1;
	}
	ll mul=1;
	fr(i,0,len-1){
		if(nxt[i][len]<(x+i)%len) return 0;
		ll tmp=(min(n/2,nxt[i][len])-(x+i)%len)/len+1;
		mul=mul*tmp%mod;
	}
	return mul;
}
int main(){
	n=read();
	fr(i,0,n) lim[i]=read();
	invv[1]=1;
	fr(i,2,n) invv[i]=(mod-mod/i)*invv[mod%i]%mod;
	fr(j,1,n+1){
		pfr(i,n,0){
			if((i+j)>n) nxt[i][j]=lim[i];
			else nxt[i][j]=min(lim[i],nxt[i+j][j]);
		}
	}
	fr(len,1,n){
		fr(i,0,n){
			a[i]=(min(n/2,nxt[i][len])-i)/len+1;
			if(a[i]<=0) a[i]=1;
		}
		ll mul=1,sum=0;
		fr(i,0,len-1) sum+=(nxt[i][len]>=i);
		fr(i,0,len-1) mul=mul*a[i]%mod;
		fr(k,1,n-len+1){
			if(lim[k-1]<(k-1)) break;
			sum-=(nxt[k-1][len]>=(k-1));
			sum+=(nxt[k+len-1][len]>=(k+len-1));
			mul=mul*invv[a[k-1]]%mod*a[k+len-1]%mod;
			if(sum==len){
				if((k+len-1)>=(n+1)/2) ans=(ans+1)%mod;
				else ans=(ans+mul)%mod;
			}
		}
	}
	bl ck=1;
	fr(i,0,n) if(lim[i]<i) ck=0;
	if(ck) ans=(ans-n+1+mod)%mod;
	fr(len,1,n){
		ans=(ans+solve2(0,len))%mod;
		if(len%2==0&&len/2<=lim[0]) ans=(ans+solve2(len/2,len))%mod;
	}
	write(ans);
}
/*
5
0 5 5 5 5 5
ans:
17
*/