A sequence $\{a_n\}$ is defined as follows: $a_1 = 1$ and $a_{n+1} = 420a_n - 69$ for all positive integers $n$. The number of squares in this sequence is $k$. Enter $k$. (If there are infinitely many square numbers in the sequence, enter 999.)
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Tags: number theory, algebra, recurrence relation
A sequence $\{a_n\}$ is defined as follows: $a_1 = 1$ and $a_{n+1} = 420a_n - 69$ for all positive integers $n$. The number of squares in this sequence is $k$. Enter $k$. (If there are infinitely many square numbers in the sequence, enter 999.)