The parent function is also called generating function or generating function. There are many kinds. The most common is the ordinary generating function.

Given an infinite sequence (A0, A 1, A2 ... one; A ...) is called f (x) = A0+a1x1+a2x2+...+anxn+ ...

Use simple things in middle school mathematics. The combination symbol of the sequence (c) n, r) can't be typed, and it can be regarded as generated by the function (1+x) n instead of taking r from n, so (1+x) n is called the generating function of this sequence. It is mainly used for the recursion of series and the counting of rearrangeable combinations. It is enough to know some simple operations in the competition. Combinatorial mathematics for college mathematics majors should be specialized and widely used in probability theory and mathematical physics methods.