C++ :

#include<iostream>
#include<iomanip>
using namespace std;
int a[21][21];
int main()
{
	int n;
	cin>>n;
	int t=1,k=1,x=2,y=0;
	while (t<=n*(n+1)/2)
	{
		while (x-1>=1 && y+1<=n) { a[--x][++y]=k++; t++; }
		a[x][++y]=k++;
		t++;
		while (x+1<=n && y-1>=1) { a[++x][--y]=k++; t++; }
		a[++x][y]=k++;
		t++;
	}
	for (int i=1; i<=n; i++)
	{
		for (int j=1; j<=n-i+1; j++) cout<<setw(4)<<a[i][j];
		cout<<endl;
	}
	return 0;
}