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I’ve post it here as another answer. No worries.

Thank you so much!!! But why 4x4x10 and why S1=0

We need to find out the possible factors, S1 have to be 0 when n=1 otherwise u1 will not match. 4x4x10 is a reasonable guess based on the S. 0, 10, 40, 160, these numbers will imply you the factor 4 and 10, (10 is part of 10/3). Once you do it in direct method, you need to try all the possibilities and test them.