Blue Bridge Cup Serpentine Filling

At the beginning, we made it together, but later found that the most direct law is the number sequence $a_i$(The value of the i-th row and the i-th column) and $a_i$The difference is an arithmetic series.
So $a_n=2n(n-1)+1$ , the process is as follows

Staggered addition method
a2-a1=4
a3-a2=8
a4-a3=12
·······
an-an-1=4(n-1)
add up to get an=a1+(4+8+… +4(n-1))

Answer: 761

#include<iostream>
using namespace std;
int main(){
    
    
    int n;
    cin>>n;
    cout<<2*n*(n-1)+1;
    return 0;
}

#include<iostream>
using namespace std;
int sum(int n){
    
    //计算1+2+...+n
    if(n==1)
        return 1;
    return sum(n-1)+n;
}
int main(){
    
    
    int n;
    // cout<<sum(6);
    cin>>n;
    cout<<sum(2*n-2)+1+(n-1);
    return 0;
}