EN
Melham discovered the Fibonacci identity
$F_{n+1}F_{n+2}F_{n+6} - F³_{n+3} = (-1)ⁿFₙ$.
He then considered the generalized sequence Wₙ where W₀ = a, W₁ = b, and $Wₙ = pW_{n-1} + qW_{n-2}$ and a, b, p and q are integers and q ≠ 0. Letting e = pab - qa² - b², he proved the following identity:
$W_{n+1}W_{n+2}W_{n+6} - W³_{n+3} = eq^{n+1}(p³W_{n+2} - q²W_{n+1})$.
There are similar differences of products of Fibonacci numbers, like this one discovered by Fairgrieve and Gould:
$FₙF_{n+4}F_{n+5} - F³_{n+3} = (-1)^{n+1}F_{n+6}$.
We prove similar identities. For example, a generalization of Fairgrieve and Gould's identity is
$WₙW_{n+4}W_{n+5} - W³_{n+3} = eqⁿ(p³W_{n+4} - qW_{n+5})$.