#include<iostream.h>
int  i,j;
long a[101][101],n;
 int main(){
    cin>>n;
   for(i=1;i<n+1;i++)
 {   a[i][n]=i*(i+1)/2;
  }
   for(i=1;i<n;i++)
 {  for(j=n-1;j>=i;j--)
  {  a[i][j]=a[i][j+1]+n-j+i-1;
   }
 }
   for(i=2;i<n+1;i++)
 {  for(j=i-1;j>0;j--)
  {  a[i][j]=a[i][j+1]+n+j-i;
   }
 }
   for(i=1;i<n+1;i++)
 { for(j=1;j<n+1;j++)
    cout<<a[i][j]<<" ";
    cout<<"\n";
  }
 return 0;
}

This method is easy but very interesting!

Nice, but there's no need in arrays if you're trying to use some math. My solution uses just seven integers and that's enough.