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Tokens and products in the board

Source: Cono Sur Math Olympiad 2020 #5

December 4, 2020
ProductsOperationInvariantscono sur

Problem Statement

There is a pile with 1515 coins on a table. At each step, Pedro choses one of the piles in the table with a>1a>1 coins and divides it in two piles with b1b\geq1 and c1c\geq1 coins and writes in the board the product abcabc. He continues until there are 1515 piles with 11 coin each. Determine all possible values that the final sum of the numbers in the board can have.