Sentinel intr-o maniera mai ciudata

Code:

#include<iostream.h>
#include<conio.h>
#include<iomanip.h>
int n,d,ok,b[100],i,k,j,x,a[20][20];
void main()
{ cout<<"n=";cin>>n;
b[1]=2;
k=2;
x=3;
while(k<=n*n) { ok=1;
for(d=2;d<=x/2;d++) if(x%d==0) ok=0;
if(ok) b[k++]=x;
x++;
}
x=1;
for(k=1;k<=n/2+1;k++) { for(j=k;j<=n-k+1;j++) a[k][j]=b[x++];
for(i=k+1;i<=n-k+1;i++) a[i][n-k+1]=b[x++];
for(j=n-k;j>=k;j--) a[n-k+1][j]=b[x++];
for(i=n-k;i>k;i--) a[i][k]=b[x++];
}
for(i=1;i<=n;i++)
{ for(j=1;j<=n;j++) cout<<setw(2)<<a[i][j]<<" ";
cout<<endl;
}
getch();
}

I am very happy because find this info thank you very much people!!!)