Following Euler, we define a partition of the positive integer n as a representation of n as a sum of positive integers, in which order is unimportant.
The partitions of 4 are 4 = 3+1 = 2+2 = 2+1+1 = 1+1+1+1. The number of partitions of n is denoted by p(n); thus, p(4) = 5. For convenience,we define p(0) = 1.