#include<bits/stdc++.h>
#define ll long long
#pragma GCC optimize(2)
#define un unsigned
#define int long long
#define db double
#define st string
#define ct const
#define xh(a,b,c) for(int a=b;a<=c;a++)
#define wx while(1)
#define dn(a,b,c) for(int a=b;a>=c;a--)
using namespace std;
int f[1000010],n;
signed main(){
	cin>>n;
	f[1]=1,f[2]=2;
	xh(i,3,n)f[i]=(f[i-1]+f[i-2])%15746;
	cout<<f[n];
	return 0;
}

#include<bits/stdc++.h> using namespace std; long long n,i,a[1050000]; int main(){ ios::sync_with_stdio(0); cin.tie(0); cout.tie(0); cin>>n; a[1]=1; a[2]=2; for(i=3;i<=n;i++) a[i]=(a[i-1]+a[i-2])%15746; cout<<a[n]; return 0; }

就是斐波那契数列

#include<bits/stdc++.h>
using namespace std;
long n,i,a[1000500];
int main()
{
   cin>>n;
   a[1]=1;
   a[2]=2;
   for(i=3;i<=n;i++)a[i]=(a[i-1]+a[i-2])%15746;
   cout<<a[n];
   return 0;
}