MathDB
Sum of partitions

Source: China TST 1989, problem 8

June 27, 2005
combinatorics unsolvedcombinatorics

Problem Statement

nN\forall n \in \mathbb{N}, P(n)P(n) denotes the number of the partition of nn as the sum of positive integers (disregarding the order of the parts), e.g. since 4=1+1+1+1=1+1+2=1+3=2+2=44 = 1+1+1+1 = 1+1+2 = 1+3 = 2+2 = 4, so P(4)=5P(4)=5. "Dispersion" of a partition denotes the number of different parts in that partitation. And denote q(n)q(n) is the sum of all the dispersions, e.g. q(4)=1+2+2+1+1=7q(4)=1+2+2+1+1=7. n1n \geq 1. Prove that (1) q(n)=1+i=1n1P(i).q(n) = 1 + \sum^{n-1}_{i=1} P(i). (2) 1+i=1n1P(i)2nP(n)1 + \sum^{n-1}_{i=1} P(i) \leq \sqrt{2} \cdot n \cdot P(n).