# Mixed Sequence Need help!

Algebra Level pending

an is arithmetic sequence that a1=2 and a1<a2<a3<.....<an suppoed that a2,a4,a8 is in geometric sequence also then find n such that (Zigma [(ai)-1]^3) i=1 to n )/(zigma (ai)^3) i=1 to n )=391/450 Anyone give me a nice solution pleaseee^__^

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