Number of integer partitions

An integer partition of n is a weakly decreasing list of positive integers which sum to n.

For example, there are 7 integer partitions of 5:

[5], [4,1], [3,2], [3,1,1], [2,2,1], [2,1,1,1], [1,1,1,1,1].

Write a function which returns the number of integer partitions of n. The function should be able to find the number of integer partitions of n for n at least as large as 100.