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Generating function and partitions

Source: Iran 3rd round 2013- Combinatorics exam problem 1

September 18, 2014
functioncombinatorics unsolvedcombinatorics

Problem Statement

Assume that the following generating function equation is correct, prove the following statement: Πi=1(1+x3i)Πj=1(1x6j+3)=1\Pi_{i=1}^{\infty} (1+x^{3i})\Pi_{j=1}^{\infty} (1-x^{6j+3})=1 Statement: The number of partitions of nn to numbers not of the form 6k+16k+1 or 6k16k-1 is equal to the number of partitions of nn in which each summand appears at least twice. (10 points) Proposed by Morteza Saghafian