打印出杨辉三角形（要求打印出前15行）。(杨辉三角最本质的特征是，它的两条斜边都是由数字1组成的，而其余的数则是等于它肩上的两个数之和。)

Print out the Yang Hui triangle (requires printing the first 15 lines). (The most essential feature of the Yang Hui triangle is that its two hypotenuses are composed of the number 1, and the rest are equal to the sum of the two numbers on its shoulder.)