
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Given $S_n$ is the sum of the first $n$ terms of a geometric sequence $\{a_n\}$ and it's known that $S_3 = \frac {3}{2}$ and $S_6 = \frac {21}{16}$, with $b_n = \lambda a_n - n^2$.
(Ⅰ) Find the general term formula $a_n$ for the sequence $\{a_n\}$;
(Ⅱ) If the sequence $\{b_n\}$ is monotonically decreasing, find the range of the real number $\lambda$.

Present the answer in LaTex format: \boxed{Your answer}
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