A sequence ana_nan satisfies an+1=kana_{n+1} = k a_nan+1=kan and ∑n=1∞an=4\sum_{n=1}^{\infty} a_n = 4∑n=1∞an=4 and ∑n=1∞an2=8\sum_{n=1}^{\infty} a_n^2 = 8∑n=1∞an2=8. What is a1a_1a1?
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