Here is a regular array of triangles First line: 1 The second line 1 Third line: 1 2 1 The fourth line: 1 3 3 1 The fifth line: 1 4 6 4 1 The sixth line; 1 5 10 10 5 1 . What is the third number from the left of line 1997 Not only the answer, but also the method,

Here is a regular array of triangles First line: 1 The second line 1 Third line: 1 2 1 The fourth line: 1 3 3 1 The fifth line: 1 4 6 4 1 The sixth line; 1 5 10 10 5 1 . What is the third number from the left of line 1997 Not only the answer, but also the method,

The answer is 1991010. The n-th line of this is the coefficient in front of (x + 1) ^ (n-1). From left to right, it is high order to low order, or from low order to high order. Anyway, it comes in order. For example, the fifth line (x + 1) ^ 4 = x ^ 4 + 4x ^ 3 + 6x ^ 2 + 4x + 1 is exactly the coefficient of 1.464.1, so the third number from the left of line 1997 is (x + 1) ^ 1996