The Twelve Days of Christmas (A Mathematical Solution)

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Libre Office (OS: Ubuntu)

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http://www.freexmasmp3.com/

Lyrics
https://en.wikipedia.org/wiki/The_Twelve_Days_of_Christmas_(song)

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Lemma 1
https://en.wikipedia.org/wiki/Triangular_number

Lemma 2
https://en.wikipedia.org/wiki/Square_pyramidal_number