Find the mistake in the below maths equations

A = 2
A(A-1) = 2(A-1)
A2-A = 2A-2
A2-2A = A-2
A(A-2) = A-2
A = 1

Can you find the odd number in the following?

2716, 4135, 5321 and 7145

I have an eye but still cannot see.

Who am I?

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Things are just as they seem, right? Well, check again.
Can you count the number of tigers in this picture ?

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In how many different ways you can climb 10 stairs?

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This is a classy optical illusion puzzle. What more you can find except bricks in the image below?