Introduction:
The given expression is n^2 * 2n * [1 2 3.... (n-1)]. In this question, we need to find the value of this expression.

Calculation:
To solve this expression, we need to break it down into individual parts and then calculate their values.

Part 1: n^2
The value of n^2 is simply n multiplied by itself. So, if n=2, then n^2=4. If n=3, then n^2=9. And so on.

Part 2: 2n
The value of 2n is simply twice the value of n. So, if n=2, then 2n=4. If n=3, then 2n=6. And so on.

Part 3: [1 2 3.... (n-1)]
This part is a bit tricky. The expression [1 2 3.... (n-1)] simply means a sequence of numbers starting from 1 and going up to (n-1). For example, if n=5, then [1 2 3 4]=1+2+3+4=10.

To calculate the value of [1 2 3.... (n-1)], we can use a formula. The formula is: sum of first n natural numbers = n*(n+1)/2. So, if n=5, then [1 2 3 4]=5*6/2=15.

Final Calculation:
Now that we have calculated the values of all three parts, we can simply multiply them together to get the final answer.

n^2 * 2n * [1 2 3.... (n-1)] = n^2 * 2n * sum of first (n-1) natural numbers

= n * n * 2 * n * (n-1) * (n-1+1)/2

= n^2 * 2n * (n-1) * n/2

= n^3 * (n-1)

Conclusion:
Therefore, the value of n^2 * 2n * [1 2 3.... (n-1)] is n^3 * (n-1).