按照古希腊三角几何，如果一定数目的卵石可以排列成对称的三角几何图形，则该数字被称为“三角形数”。例如，前10个三角形数分别为0，1，3，6，10，15，21，28，36，45。-In accordance with the ancient Greek trigonometry, if a certain number of pebbles can be arranged in a symmetrical triangle geometry, the number is called " triangular number. For example, the 10 triangles were 0,1,3,6,10,15,21,28,36,45.