輸出數字的形狀為三角形

#include <stdio.h>
void main()
{
	int i =1,a = 2, b= 0, n = 0; 
	for (int j = 0;i+b<=21;j++)
	{
		n = i;
		printf("%-3d",n);
		for (int k = 0;n+a+k<=21;k++)
		{
			n =n+a+k;			
			printf("%-3d",n);			
		}
		printf("\n");
		b++;
		i = i+b;
		a++;
	}
}