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In this Wikipedia entry on Cassini's identity, I saw this equation:

$F_{n-1}F_{n+1}-F^2_n=(-1)^n$

$F^2_n$, what does that mean? Is it a summation signs for n to 2? I don't know what it means.

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    ah ok thanks you could have answered instead2012-11-18

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$F_n^2$ is the square of the $n^{\text{th}}$ Fibonacci number.