For example, in the sequence an, A 1 = 1, A2 = 2, A3 = 3, and the recurrence formula is an=n(n is a positive integer).

For example, in the sequence bn, B 1 = 1, B2 = 2, B3 = 4, B4 = 8, each term is the previous term multiplied by 2, and the recurrence formula is the (n- 1) power of bn=2.

Recursive formula is a fixed relationship between the number of items and the value of items.