Putnam 2015 A2

Let $a_0=1$ , $a_1=2$ , and $a_n=4a_{n-1}-a_{n-2}$ for $n\geq 2$ . Find an odd prime factor of $a_{2015}$ .

Curated text Kedlaya Putnam archive. Quoted with source.

Solutions

Human solution Solution 1 by Manjul Bhargava, Kiran Kedlaya and Lenny Ng

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