Find the Nth Term of the Matrix?

Hello. I'm unable to find the nth term of this matrix. I have found A^2, A^3, and A^4 (as well as A^5 to check my general equation). I cannot find the relationship between 6a^2, 10a^3, and 15a^4 (A^3, A^4. A^5), and am very confused. Any help would be appreciated!

2020-10-21T21:50:01Z

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2017-04-11T00:37:33.809Z