3. [2 marks] Find the closed form generating function for 133011), the number of partitions of the integer n in which each part can be used at most 3 times. For example 1 + 1 + 1 + 1 + 2 + 2 + 3 is allowed since the 1s, 2s, and 3s are used at most 3 times each, but 1 + 1 + 1 + 1 + 2 + 2 + 3 is not allowed since this partition uses four 1s (Le. the 1 is used more than 3 times)