# $$5 a_n a_{n+1}=a_n - a_{n+1}$$

Calculus Level 2

The sequence $$\{a_n\}$$ satisfies $$a_1 = 1$$ and $5 a_n a_{n+1}=a_n - a_{n+1} \text{ for } n \geq 1.$ What is the value of $$a_{11}?$$

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